| Message ID | 1428046825-6905-1-git-send-email-wanpeng.li@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 03/04/2015 09:40, Wanpeng Li wrote: > There are two scenarios for the requirement of collapsing small sptes > into large sptes. > - dirty logging tracks sptes in 4k granularity, so large sptes are split, > the large sptes will be reallocated in the destination machine and the > guest in the source machine will be destroyed when live migration successfully. > However, the guest in the source machine will continue to run if live migration > fail due to some reasons, the sptes still keep small which lead to bad > performance. > - our customers write tools to track the dirty speed of guests by EPT D bit/PML > in order to determine the most appropriate one to be live migrated, however > sptes will still keep small after tracking dirty speed. > > This patch introduce lazy collapse small sptes into large sptes, the memory region > will be scanned on the ioctl context when dirty log is stopped, the ones which can > be collapsed into large pages will be dropped during the scan, it depends the on > later #PF to reallocate all large sptes. > > Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com> > Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> > --- > v2 -> v3: > * update comments > * fix infinite for loop > v1 -> v2: > * use 'bool' instead of 'int' > * add more comments > * fix can not get the next spte after drop the current spte > > arch/x86/include/asm/kvm_host.h | 2 ++ > arch/x86/kvm/mmu.c | 73 +++++++++++++++++++++++++++++++++++++++++ > arch/x86/kvm/x86.c | 19 +++++++++++ > 3 files changed, 94 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 30b28dc..91b5bdb 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -854,6 +854,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, > void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); > void kvm_mmu_slot_remove_write_access(struct kvm *kvm, > struct kvm_memory_slot *memslot); > +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, > + struct kvm_memory_slot *memslot); > void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, > struct kvm_memory_slot *memslot); > void kvm_mmu_slot_largepage_remove_write_access(struct kvm *kvm, > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index cee7592..ba002a0 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -4465,6 +4465,79 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, > kvm_flush_remote_tlbs(kvm); > } > > +static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, > + unsigned long *rmapp) > +{ > + u64 *sptep; > + struct rmap_iterator iter; > + int need_tlb_flush = 0; > + pfn_t pfn; > + struct kvm_mmu_page *sp; > + > + for (sptep = rmap_get_first(*rmapp, &iter); sptep;) { > + BUG_ON(!(*sptep & PT_PRESENT_MASK)); > + > + sp = page_header(__pa(sptep)); > + pfn = spte_to_pfn(*sptep); > + > + /* > + * Lets support EPT only for now, there still needs to figure > + * out an efficient way to let these codes be aware what mapping > + * level used in guest. > + */ > + if (sp->role.direct && > + !kvm_is_reserved_pfn(pfn) && > + PageTransCompound(pfn_to_page(pfn))) { > + drop_spte(kvm, sptep); > + sptep = rmap_get_first(*rmapp, &iter); > + need_tlb_flush = 1; > + } else > + sptep = rmap_get_next(&iter); > + } > + > + return need_tlb_flush; > +} > + > +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, > + struct kvm_memory_slot *memslot) > +{ > + bool flush = false; > + unsigned long *rmapp; > + unsigned long last_index, index; > + gfn_t gfn_start, gfn_end; > + > + spin_lock(&kvm->mmu_lock); > + > + gfn_start = memslot->base_gfn; > + gfn_end = memslot->base_gfn + memslot->npages - 1; > + > + if (gfn_start >= gfn_end) > + goto out; > + > + rmapp = memslot->arch.rmap[0]; > + last_index = gfn_to_index(gfn_end, memslot->base_gfn, > + PT_PAGE_TABLE_LEVEL); > + > + for (index = 0; index <= last_index; ++index, ++rmapp) { > + if (*rmapp) > + flush |= kvm_mmu_zap_collapsible_spte(kvm, rmapp); > + > + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { > + if (flush) { > + kvm_flush_remote_tlbs(kvm); > + flush = false; > + } > + cond_resched_lock(&kvm->mmu_lock); > + } > + } > + > + if (flush) > + kvm_flush_remote_tlbs(kvm); > + > +out: > + spin_unlock(&kvm->mmu_lock); > +} > + > void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, > struct kvm_memory_slot *memslot) > { > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 50861dd..a6cd10b 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7647,6 +7647,25 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, > new = id_to_memslot(kvm->memslots, mem->slot); > > /* > + * Dirty logging tracks sptes in 4k granularity, so large sptes are > + * split, the large sptes will be reallocated in the destination > + * machine and the guest in the source machine will be destroyed > + * when live migration successfully. However, the guest in the source > + * machine will continue to run if live migration fail due to some > + * reasons, the sptes still keep small which lead to bad performance. > + * > + * Lazy collapse small sptes into large sptes is intended to handle > + * this, the memory region will be scanned on the ioctl context when > + * dirty log is stopped, the ones which can be collapsed into large > + * pages will be dropped during the scan, it depends the on later #PF > + * to reallocate all large sptes. > + */ > + if ((change != KVM_MR_DELETE) && > + (old->flags & KVM_MEM_LOG_DIRTY_PAGES) && > + !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) > + kvm_mmu_zap_collapsible_sptes(kvm, new); > + > + /* > * Set up write protection and/or dirty logging for the new slot. > * > * For KVM_MR_DELETE and KVM_MR_MOVE, the shadow pages of old slot have > Applied just with editing of the comments and commit message. Thanks to you and Xiao. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Apr 3, 2015 at 12:40 AM, Wanpeng Li <wanpeng.li@linux.intel.com> wrote: > > There are two scenarios for the requirement of collapsing small sptes > into large sptes. > - dirty logging tracks sptes in 4k granularity, so large sptes are split, > the large sptes will be reallocated in the destination machine and the > guest in the source machine will be destroyed when live migration successfully. > However, the guest in the source machine will continue to run if live migration > fail due to some reasons, the sptes still keep small which lead to bad > performance. > - our customers write tools to track the dirty speed of guests by EPT D bit/PML > in order to determine the most appropriate one to be live migrated, however > sptes will still keep small after tracking dirty speed. > > This patch introduce lazy collapse small sptes into large sptes, the memory region > will be scanned on the ioctl context when dirty log is stopped, the ones which can > be collapsed into large pages will be dropped during the scan, it depends the on > later #PF to reallocate all large sptes. > > Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com> > Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> Hi, apologies for late review (vacation), but wanted to bring attention to a few matters: > > --- > v2 -> v3: > * update comments > * fix infinite for loop > v1 -> v2: > * use 'bool' instead of 'int' > * add more comments > * fix can not get the next spte after drop the current spte > > arch/x86/include/asm/kvm_host.h | 2 ++ > arch/x86/kvm/mmu.c | 73 +++++++++++++++++++++++++++++++++++++++++ > arch/x86/kvm/x86.c | 19 +++++++++++ > 3 files changed, 94 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 30b28dc..91b5bdb 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -854,6 +854,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, > void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); > void kvm_mmu_slot_remove_write_access(struct kvm *kvm, > struct kvm_memory_slot *memslot); > +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, > + struct kvm_memory_slot *memslot); > void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, > struct kvm_memory_slot *memslot); > void kvm_mmu_slot_largepage_remove_write_access(struct kvm *kvm, > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index cee7592..ba002a0 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -4465,6 +4465,79 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, > kvm_flush_remote_tlbs(kvm); > } > > +static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, > + unsigned long *rmapp) > +{ > + u64 *sptep; > + struct rmap_iterator iter; > + int need_tlb_flush = 0; > + pfn_t pfn; > + struct kvm_mmu_page *sp; > + > + for (sptep = rmap_get_first(*rmapp, &iter); sptep;) { > + BUG_ON(!(*sptep & PT_PRESENT_MASK)); > + > + sp = page_header(__pa(sptep)); > + pfn = spte_to_pfn(*sptep); > + > + /* > + * Lets support EPT only for now, there still needs to figure > + * out an efficient way to let these codes be aware what mapping > + * level used in guest. > + */ > + if (sp->role.direct && > + !kvm_is_reserved_pfn(pfn) && > + PageTransCompound(pfn_to_page(pfn))) { Not your fault, but PageTransCompound is very unhappy naming, as it also yields true for PageHuge. Suggestion: document this check covers static hugetlbfs, or switch to PageCompound() check. A slightly bolder approach would be to refactor and reuse the nearly identical check done in transparent_hugepage_adjust, instead of open-coding here. In essence this code is asking for the same check, plus the out-of-band check for static hugepages. > + drop_spte(kvm, sptep); > + sptep = rmap_get_first(*rmapp, &iter); > + need_tlb_flush = 1; > + } else > + sptep = rmap_get_next(&iter); > + } > + > + return need_tlb_flush; > +} > + > +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, > + struct kvm_memory_slot *memslot) > +{ > + bool flush = false; > + unsigned long *rmapp; > + unsigned long last_index, index; > + gfn_t gfn_start, gfn_end; > + > + spin_lock(&kvm->mmu_lock); > + > + gfn_start = memslot->base_gfn; > + gfn_end = memslot->base_gfn + memslot->npages - 1; > + > + if (gfn_start >= gfn_end) > + goto out; I don't understand the value of this check here. Are we looking for a broken memslot? Shouldn't this be a BUG_ON? Is this the place to care about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e. 2^31. A 64 bit overflow would be caused by a gigantic gfn_start which would be trouble in many other ways. All this to say: please remove the above 5 lines and make code simpler. > + > + rmapp = memslot->arch.rmap[0]; > + last_index = gfn_to_index(gfn_end, memslot->base_gfn, > + PT_PAGE_TABLE_LEVEL); > + > + for (index = 0; index <= last_index; ++index, ++rmapp) { One could argue that the cleaner iteration should be over the gfn space covered by the memslot, thus leaving the gfn <--> rmap <--> spte interactions hidden under the hood of __gfn_to_rmap. That yields much cleaner (IMHO) code: for (gfn = memslot->base_gfn; gfn <= memslot->base_gfn + memslot->npages; gfn++) { flush |= kvm_mmu_zap_collapsible_spte(kvm, __gfn_to_rmap(gfn, 1, memslot)); .... Now you can also get rid of index, last_index and rmapp. And more importantly, the code is more understandable, and follows pattern as established in x86/kvm/mmu. > + if (*rmapp) > + flush |= kvm_mmu_zap_collapsible_spte(kvm, rmapp); > + > + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { > + if (flush) { > + kvm_flush_remote_tlbs(kvm); > + flush = false; > + } > + cond_resched_lock(&kvm->mmu_lock); Relinquishing this spinlock is problematic, because commit_memory_region has not gotten around to removing write protection. Are you certain no new write-protected PTEs will be inserted by a racing fault that sneaks in while the spinlock is relinquished? If that can happen, you can decide that does not really matter, or the collapsing is best effort, but either of those decisions should be documented. If you absolutely want to go for complete removal of PTEs, then you need to restart the loop (costly!), or retain you structure that iterates on the rmapp array, but restart from the beginning after each spinlock removal (less costly, but not happy). Thanks Andres > + } > + } > + > + if (flush) > + kvm_flush_remote_tlbs(kvm); > + > +out: > + spin_unlock(&kvm->mmu_lock); > +} > + > void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, > struct kvm_memory_slot *memslot) > { > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 50861dd..a6cd10b 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7647,6 +7647,25 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, > new = id_to_memslot(kvm->memslots, mem->slot); > > /* > + * Dirty logging tracks sptes in 4k granularity, so large sptes are > + * split, the large sptes will be reallocated in the destination > + * machine and the guest in the source machine will be destroyed > + * when live migration successfully. However, the guest in the source > + * machine will continue to run if live migration fail due to some > + * reasons, the sptes still keep small which lead to bad performance. > + * > + * Lazy collapse small sptes into large sptes is intended to handle > + * this, the memory region will be scanned on the ioctl context when > + * dirty log is stopped, the ones which can be collapsed into large > + * pages will be dropped during the scan, it depends the on later #PF > + * to reallocate all large sptes. > + */ > + if ((change != KVM_MR_DELETE) && > + (old->flags & KVM_MEM_LOG_DIRTY_PAGES) && > + !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) > + kvm_mmu_zap_collapsible_sptes(kvm, new); > + > + /* > * Set up write protection and/or dirty logging for the new slot. > * > * For KVM_MR_DELETE and KVM_MR_MOVE, the shadow pages of old slot have > -- > 1.9.1 > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/11/2015 02:05 AM, Andres Lagar-Cavilla wrote: > On Fri, Apr 3, 2015 at 12:40 AM, Wanpeng Li <wanpeng.li@linux.intel.com> wrote: >> >> There are two scenarios for the requirement of collapsing small sptes >> into large sptes. >> - dirty logging tracks sptes in 4k granularity, so large sptes are split, >> the large sptes will be reallocated in the destination machine and the >> guest in the source machine will be destroyed when live migration successfully. >> However, the guest in the source machine will continue to run if live migration >> fail due to some reasons, the sptes still keep small which lead to bad >> performance. >> - our customers write tools to track the dirty speed of guests by EPT D bit/PML >> in order to determine the most appropriate one to be live migrated, however >> sptes will still keep small after tracking dirty speed. >> >> This patch introduce lazy collapse small sptes into large sptes, the memory region >> will be scanned on the ioctl context when dirty log is stopped, the ones which can >> be collapsed into large pages will be dropped during the scan, it depends the on >> later #PF to reallocate all large sptes. >> >> Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com> >> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> > > Hi, apologies for late review (vacation), but wanted to bring > attention to a few matters: No problem, your comments are really valuable to us. :) > >> >> --- >> v2 -> v3: >> * update comments >> * fix infinite for loop >> v1 -> v2: >> * use 'bool' instead of 'int' >> * add more comments >> * fix can not get the next spte after drop the current spte >> >> arch/x86/include/asm/kvm_host.h | 2 ++ >> arch/x86/kvm/mmu.c | 73 +++++++++++++++++++++++++++++++++++++++++ >> arch/x86/kvm/x86.c | 19 +++++++++++ >> 3 files changed, 94 insertions(+) >> >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> index 30b28dc..91b5bdb 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -854,6 +854,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, >> void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); >> void kvm_mmu_slot_remove_write_access(struct kvm *kvm, >> struct kvm_memory_slot *memslot); >> +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >> + struct kvm_memory_slot *memslot); >> void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, >> struct kvm_memory_slot *memslot); >> void kvm_mmu_slot_largepage_remove_write_access(struct kvm *kvm, >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index cee7592..ba002a0 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -4465,6 +4465,79 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, >> kvm_flush_remote_tlbs(kvm); >> } >> >> +static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, >> + unsigned long *rmapp) >> +{ >> + u64 *sptep; >> + struct rmap_iterator iter; >> + int need_tlb_flush = 0; >> + pfn_t pfn; >> + struct kvm_mmu_page *sp; >> + >> + for (sptep = rmap_get_first(*rmapp, &iter); sptep;) { >> + BUG_ON(!(*sptep & PT_PRESENT_MASK)); >> + >> + sp = page_header(__pa(sptep)); >> + pfn = spte_to_pfn(*sptep); >> + >> + /* >> + * Lets support EPT only for now, there still needs to figure >> + * out an efficient way to let these codes be aware what mapping >> + * level used in guest. >> + */ >> + if (sp->role.direct && >> + !kvm_is_reserved_pfn(pfn) && >> + PageTransCompound(pfn_to_page(pfn))) { > > Not your fault, but PageTransCompound is very unhappy naming, as it > also yields true for PageHuge. Suggestion: document this check covers > static hugetlbfs, or switch to PageCompound() check. > > A slightly bolder approach would be to refactor and reuse the nearly > identical check done in transparent_hugepage_adjust, instead of > open-coding here. In essence this code is asking for the same check, > plus the out-of-band check for static hugepages. I agree. > > >> + drop_spte(kvm, sptep); >> + sptep = rmap_get_first(*rmapp, &iter); >> + need_tlb_flush = 1; >> + } else >> + sptep = rmap_get_next(&iter); >> + } >> + >> + return need_tlb_flush; >> +} >> + >> +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >> + struct kvm_memory_slot *memslot) >> +{ >> + bool flush = false; >> + unsigned long *rmapp; >> + unsigned long last_index, index; >> + gfn_t gfn_start, gfn_end; >> + >> + spin_lock(&kvm->mmu_lock); >> + >> + gfn_start = memslot->base_gfn; >> + gfn_end = memslot->base_gfn + memslot->npages - 1; >> + >> + if (gfn_start >= gfn_end) >> + goto out; > > I don't understand the value of this check here. Are we looking for a > broken memslot? Shouldn't this be a BUG_ON? Is this the place to care > about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e. > 2^31. A 64 bit overflow would be caused by a gigantic gfn_start which > would be trouble in many other ways. > > All this to say: please remove the above 5 lines and make code simpler. Yes, this check is unnecessary indeed. > >> + >> + rmapp = memslot->arch.rmap[0]; >> + last_index = gfn_to_index(gfn_end, memslot->base_gfn, >> + PT_PAGE_TABLE_LEVEL); >> + >> + for (index = 0; index <= last_index; ++index, ++rmapp) { > > One could argue that the cleaner iteration should be over the gfn > space covered by the memslot, thus leaving the gfn <--> rmap <--> spte > interactions hidden under the hood of __gfn_to_rmap. That yields much > cleaner (IMHO) code: > > for (gfn = memslot->base_gfn; gfn <= memslot->base_gfn + > memslot->npages; gfn++) { > flush |= kvm_mmu_zap_collapsible_spte(kvm, __gfn_to_rmap(gfn, > 1, memslot)); > .... > > Now you can also get rid of index, last_index and rmapp. And more > importantly, the code is more understandable, and follows pattern as > established in x86/kvm/mmu. Do not have strong opinion on it. Current code also has this style, please refer to kvm_mmu_slot_remove_write_access(). > >> + if (*rmapp) >> + flush |= kvm_mmu_zap_collapsible_spte(kvm, rmapp); >> + >> + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { >> + if (flush) { >> + kvm_flush_remote_tlbs(kvm); >> + flush = false; >> + } >> + cond_resched_lock(&kvm->mmu_lock); > > Relinquishing this spinlock is problematic, because > commit_memory_region has not gotten around to removing write > protection. Are you certain no new write-protected PTEs will be > inserted by a racing fault that sneaks in while the spinlock is > relinquished? > I do not know clearly about the problem, new spte creation will be based on the host mapping, i.e, the huge mapping on shadow page table will be sync-ed with huge mapping on host. Could you please detail the problem? Wanpeng, could you please post a patch to address Andres's comments? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Apr 13, 2015 at 09:45:39AM +0800, Xiao Guangrong wrote: > > >On 04/11/2015 02:05 AM, Andres Lagar-Cavilla wrote: >>On Fri, Apr 3, 2015 at 12:40 AM, Wanpeng Li <wanpeng.li@linux.intel.com> wrote: >>> >>>There are two scenarios for the requirement of collapsing small sptes >>>into large sptes. >>>- dirty logging tracks sptes in 4k granularity, so large sptes are split, >>> the large sptes will be reallocated in the destination machine and the >>> guest in the source machine will be destroyed when live migration successfully. >>> However, the guest in the source machine will continue to run if live migration >>> fail due to some reasons, the sptes still keep small which lead to bad >>> performance. >>>- our customers write tools to track the dirty speed of guests by EPT D bit/PML >>> in order to determine the most appropriate one to be live migrated, however >>> sptes will still keep small after tracking dirty speed. >>> >>>This patch introduce lazy collapse small sptes into large sptes, the memory region >>>will be scanned on the ioctl context when dirty log is stopped, the ones which can >>>be collapsed into large pages will be dropped during the scan, it depends the on >>>later #PF to reallocate all large sptes. >>> >>>Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com> >>>Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> >> >>Hi, apologies for late review (vacation), but wanted to bring >>attention to a few matters: > >No problem, your comments are really valuable to us. :) > >> >>> >>>--- >>>v2 -> v3: >>> * update comments >>> * fix infinite for loop >>>v1 -> v2: >>> * use 'bool' instead of 'int' >>> * add more comments >>> * fix can not get the next spte after drop the current spte >>> >>> arch/x86/include/asm/kvm_host.h | 2 ++ >>> arch/x86/kvm/mmu.c | 73 +++++++++++++++++++++++++++++++++++++++++ >>> arch/x86/kvm/x86.c | 19 +++++++++++ >>> 3 files changed, 94 insertions(+) >>> >>>diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >>>index 30b28dc..91b5bdb 100644 >>>--- a/arch/x86/include/asm/kvm_host.h >>>+++ b/arch/x86/include/asm/kvm_host.h >>>@@ -854,6 +854,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, >>> void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); >>> void kvm_mmu_slot_remove_write_access(struct kvm *kvm, >>> struct kvm_memory_slot *memslot); >>>+void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >>>+ struct kvm_memory_slot *memslot); >>> void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, >>> struct kvm_memory_slot *memslot); >>> void kvm_mmu_slot_largepage_remove_write_access(struct kvm *kvm, >>>diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>>index cee7592..ba002a0 100644 >>>--- a/arch/x86/kvm/mmu.c >>>+++ b/arch/x86/kvm/mmu.c >>>@@ -4465,6 +4465,79 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, >>> kvm_flush_remote_tlbs(kvm); >>> } >>> >>>+static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, >>>+ unsigned long *rmapp) >>>+{ >>>+ u64 *sptep; >>>+ struct rmap_iterator iter; >>>+ int need_tlb_flush = 0; >>>+ pfn_t pfn; >>>+ struct kvm_mmu_page *sp; >>>+ >>>+ for (sptep = rmap_get_first(*rmapp, &iter); sptep;) { >>>+ BUG_ON(!(*sptep & PT_PRESENT_MASK)); >>>+ >>>+ sp = page_header(__pa(sptep)); >>>+ pfn = spte_to_pfn(*sptep); >>>+ >>>+ /* >>>+ * Lets support EPT only for now, there still needs to figure >>>+ * out an efficient way to let these codes be aware what mapping >>>+ * level used in guest. >>>+ */ >>>+ if (sp->role.direct && >>>+ !kvm_is_reserved_pfn(pfn) && >>>+ PageTransCompound(pfn_to_page(pfn))) { >> >>Not your fault, but PageTransCompound is very unhappy naming, as it >>also yields true for PageHuge. Suggestion: document this check covers >>static hugetlbfs, or switch to PageCompound() check. >> >>A slightly bolder approach would be to refactor and reuse the nearly >>identical check done in transparent_hugepage_adjust, instead of >>open-coding here. In essence this code is asking for the same check, >>plus the out-of-band check for static hugepages. > >I agree. > >> >> >>>+ drop_spte(kvm, sptep); >>>+ sptep = rmap_get_first(*rmapp, &iter); >>>+ need_tlb_flush = 1; >>>+ } else >>>+ sptep = rmap_get_next(&iter); >>>+ } >>>+ >>>+ return need_tlb_flush; >>>+} >>>+ >>>+void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >>>+ struct kvm_memory_slot *memslot) >>>+{ >>>+ bool flush = false; >>>+ unsigned long *rmapp; >>>+ unsigned long last_index, index; >>>+ gfn_t gfn_start, gfn_end; >>>+ >>>+ spin_lock(&kvm->mmu_lock); >>>+ >>>+ gfn_start = memslot->base_gfn; >>>+ gfn_end = memslot->base_gfn + memslot->npages - 1; >>>+ >>>+ if (gfn_start >= gfn_end) >>>+ goto out; >> >>I don't understand the value of this check here. Are we looking for a >>broken memslot? Shouldn't this be a BUG_ON? Is this the place to care >>about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e. >>2^31. A 64 bit overflow would be caused by a gigantic gfn_start which >>would be trouble in many other ways. >> >>All this to say: please remove the above 5 lines and make code simpler. > >Yes, this check is unnecessary indeed. > >> >>>+ >>>+ rmapp = memslot->arch.rmap[0]; >>>+ last_index = gfn_to_index(gfn_end, memslot->base_gfn, >>>+ PT_PAGE_TABLE_LEVEL); >>>+ >>>+ for (index = 0; index <= last_index; ++index, ++rmapp) { >> >>One could argue that the cleaner iteration should be over the gfn >>space covered by the memslot, thus leaving the gfn <--> rmap <--> spte >>interactions hidden under the hood of __gfn_to_rmap. That yields much >>cleaner (IMHO) code: >> >> for (gfn = memslot->base_gfn; gfn <= memslot->base_gfn + >>memslot->npages; gfn++) { >> flush |= kvm_mmu_zap_collapsible_spte(kvm, __gfn_to_rmap(gfn, >>1, memslot)); >> .... >> >>Now you can also get rid of index, last_index and rmapp. And more >>importantly, the code is more understandable, and follows pattern as >>established in x86/kvm/mmu. > >Do not have strong opinion on it. Current code also has this style, please >refer to kvm_mmu_slot_remove_write_access(). > >> >>>+ if (*rmapp) >>>+ flush |= kvm_mmu_zap_collapsible_spte(kvm, rmapp); >>>+ >>>+ if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { >>>+ if (flush) { >>>+ kvm_flush_remote_tlbs(kvm); >>>+ flush = false; >>>+ } >>>+ cond_resched_lock(&kvm->mmu_lock); >> >>Relinquishing this spinlock is problematic, because >>commit_memory_region has not gotten around to removing write >>protection. Are you certain no new write-protected PTEs will be >>inserted by a racing fault that sneaks in while the spinlock is >>relinquished? >> > >I do not know clearly about the problem, new spte creation will be based on >the host mapping, i.e, the huge mapping on shadow page table will be >sync-ed with huge mapping on host. Could you please detail the problem? > >Wanpeng, could you please post a patch to address Andres's comments? Yeah, I will post a patch which is based on this one after merge window. :) Regards, Wanpeng Li -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, Apr 12, 2015 at 6:45 PM, Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote: > > > On 04/11/2015 02:05 AM, Andres Lagar-Cavilla wrote: >> >> On Fri, Apr 3, 2015 at 12:40 AM, Wanpeng Li <wanpeng.li@linux.intel.com> >> wrote: >>> >>> >>> There are two scenarios for the requirement of collapsing small sptes >>> into large sptes. >>> - dirty logging tracks sptes in 4k granularity, so large sptes are split, >>> the large sptes will be reallocated in the destination machine and the >>> guest in the source machine will be destroyed when live migration >>> successfully. >>> However, the guest in the source machine will continue to run if live >>> migration >>> fail due to some reasons, the sptes still keep small which lead to bad >>> performance. >>> - our customers write tools to track the dirty speed of guests by EPT D >>> bit/PML >>> in order to determine the most appropriate one to be live migrated, >>> however >>> sptes will still keep small after tracking dirty speed. >>> >>> This patch introduce lazy collapse small sptes into large sptes, the >>> memory region >>> will be scanned on the ioctl context when dirty log is stopped, the ones >>> which can >>> be collapsed into large pages will be dropped during the scan, it depends >>> the on >>> later #PF to reallocate all large sptes. >>> >>> Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com> >>> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> >> >> >> Hi, apologies for late review (vacation), but wanted to bring >> attention to a few matters: > > > No problem, your comments are really valuable to us. :) Glad to know, thanks. > > >> >>> >>> --- >>> v2 -> v3: >>> * update comments >>> * fix infinite for loop >>> v1 -> v2: >>> * use 'bool' instead of 'int' >>> * add more comments >>> * fix can not get the next spte after drop the current spte >>> >>> arch/x86/include/asm/kvm_host.h | 2 ++ >>> arch/x86/kvm/mmu.c | 73 >>> +++++++++++++++++++++++++++++++++++++++++ >>> arch/x86/kvm/x86.c | 19 +++++++++++ >>> 3 files changed, 94 insertions(+) >>> >>> diff --git a/arch/x86/include/asm/kvm_host.h >>> b/arch/x86/include/asm/kvm_host.h >>> index 30b28dc..91b5bdb 100644 >>> --- a/arch/x86/include/asm/kvm_host.h >>> +++ b/arch/x86/include/asm/kvm_host.h >>> @@ -854,6 +854,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 >>> accessed_mask, >>> void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); >>> void kvm_mmu_slot_remove_write_access(struct kvm *kvm, >>> struct kvm_memory_slot *memslot); >>> +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >>> + struct kvm_memory_slot *memslot); >>> void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, >>> struct kvm_memory_slot *memslot); >>> void kvm_mmu_slot_largepage_remove_write_access(struct kvm *kvm, >>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>> index cee7592..ba002a0 100644 >>> --- a/arch/x86/kvm/mmu.c >>> +++ b/arch/x86/kvm/mmu.c >>> @@ -4465,6 +4465,79 @@ void kvm_mmu_slot_remove_write_access(struct kvm >>> *kvm, >>> kvm_flush_remote_tlbs(kvm); >>> } >>> >>> +static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, >>> + unsigned long *rmapp) >>> +{ >>> + u64 *sptep; >>> + struct rmap_iterator iter; >>> + int need_tlb_flush = 0; >>> + pfn_t pfn; >>> + struct kvm_mmu_page *sp; >>> + >>> + for (sptep = rmap_get_first(*rmapp, &iter); sptep;) { >>> + BUG_ON(!(*sptep & PT_PRESENT_MASK)); >>> + >>> + sp = page_header(__pa(sptep)); >>> + pfn = spte_to_pfn(*sptep); >>> + >>> + /* >>> + * Lets support EPT only for now, there still needs to >>> figure >>> + * out an efficient way to let these codes be aware what >>> mapping >>> + * level used in guest. >>> + */ >>> + if (sp->role.direct && >>> + !kvm_is_reserved_pfn(pfn) && >>> + PageTransCompound(pfn_to_page(pfn))) { >> >> >> Not your fault, but PageTransCompound is very unhappy naming, as it >> also yields true for PageHuge. Suggestion: document this check covers >> static hugetlbfs, or switch to PageCompound() check. >> >> A slightly bolder approach would be to refactor and reuse the nearly >> identical check done in transparent_hugepage_adjust, instead of >> open-coding here. In essence this code is asking for the same check, >> plus the out-of-band check for static hugepages. > > > I agree. > > >> >> >>> + drop_spte(kvm, sptep); >>> + sptep = rmap_get_first(*rmapp, &iter); >>> + need_tlb_flush = 1; >>> + } else >>> + sptep = rmap_get_next(&iter); >>> + } >>> + >>> + return need_tlb_flush; >>> +} >>> + >>> +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >>> + struct kvm_memory_slot *memslot) >>> +{ >>> + bool flush = false; >>> + unsigned long *rmapp; >>> + unsigned long last_index, index; >>> + gfn_t gfn_start, gfn_end; >>> + >>> + spin_lock(&kvm->mmu_lock); >>> + >>> + gfn_start = memslot->base_gfn; >>> + gfn_end = memslot->base_gfn + memslot->npages - 1; >>> + >>> + if (gfn_start >= gfn_end) >>> + goto out; >> >> >> I don't understand the value of this check here. Are we looking for a >> broken memslot? Shouldn't this be a BUG_ON? Is this the place to care >> about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e. >> 2^31. A 64 bit overflow would be caused by a gigantic gfn_start which >> would be trouble in many other ways. >> >> All this to say: please remove the above 5 lines and make code simpler. > > > Yes, this check is unnecessary indeed. > >> >>> + >>> + rmapp = memslot->arch.rmap[0]; >>> + last_index = gfn_to_index(gfn_end, memslot->base_gfn, >>> + PT_PAGE_TABLE_LEVEL); >>> + >>> + for (index = 0; index <= last_index; ++index, ++rmapp) { >> >> >> One could argue that the cleaner iteration should be over the gfn >> space covered by the memslot, thus leaving the gfn <--> rmap <--> spte >> interactions hidden under the hood of __gfn_to_rmap. That yields much >> cleaner (IMHO) code: >> >> for (gfn = memslot->base_gfn; gfn <= memslot->base_gfn + >> memslot->npages; gfn++) { >> flush |= kvm_mmu_zap_collapsible_spte(kvm, __gfn_to_rmap(gfn, >> 1, memslot)); >> .... >> >> Now you can also get rid of index, last_index and rmapp. And more >> importantly, the code is more understandable, and follows pattern as >> established in x86/kvm/mmu. > > > Do not have strong opinion on it. Current code also has this style, please > refer to kvm_mmu_slot_remove_write_access(). > Ugh. You're right. Not your fight to pick, I guess. >> >>> + if (*rmapp) >>> + flush |= kvm_mmu_zap_collapsible_spte(kvm, >>> rmapp); >>> + >>> + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { >>> + if (flush) { >>> + kvm_flush_remote_tlbs(kvm); >>> + flush = false; >>> + } >>> + cond_resched_lock(&kvm->mmu_lock); >> >> >> Relinquishing this spinlock is problematic, because >> commit_memory_region has not gotten around to removing write >> protection. Are you certain no new write-protected PTEs will be >> inserted by a racing fault that sneaks in while the spinlock is >> relinquished? >> > > I do not know clearly about the problem, new spte creation will be based on > the host mapping, i.e, the huge mapping on shadow page table will be > sync-ed with huge mapping on host. Could you please detail the problem? > It seems that, prior to calling commit_memory_region, the new memslot with dirty_bitmap = NULL is made effective. This will ensure force_pt_level is false in tdp_page_fault, and huge mappings are observed. So all is well and I was fud'ing. N.B.: software shadow mode? > Wanpeng, could you please post a patch to address Andres's comments? > Awesome, thanks Andres
Hi Andres, On Fri, Apr 10, 2015 at 11:05:26AM -0700, Andres Lagar-Cavilla wrote: [...] >> + if (sp->role.direct && >> + !kvm_is_reserved_pfn(pfn) && >> + PageTransCompound(pfn_to_page(pfn))) { > >Not your fault, but PageTransCompound is very unhappy naming, as it >also yields true for PageHuge. Suggestion: document this check covers >static hugetlbfs, or switch to PageCompound() check. > >A slightly bolder approach would be to refactor and reuse the nearly >identical check done in transparent_hugepage_adjust, instead of >open-coding here. In essence this code is asking for the same check, >plus the out-of-band check for static hugepages. PageCompound() check still return true for both transparent huge pages and hugetlbfs pages, !PageHuge(page) && PageTransHuge(page) check can guarantee to catch the right transparent huge pages just as my old commit e76d30e20be5fc ("mm/hwpoison: fix test for a transparent huge page"). I will send a patch to fix this. > > >> + drop_spte(kvm, sptep); >> + sptep = rmap_get_first(*rmapp, &iter); >> + need_tlb_flush = 1; >> + } else >> + sptep = rmap_get_next(&iter); >> + } >> + >> + return need_tlb_flush; >> +} >> + >> +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >> + struct kvm_memory_slot *memslot) >> +{ >> + bool flush = false; >> + unsigned long *rmapp; >> + unsigned long last_index, index; >> + gfn_t gfn_start, gfn_end; >> + >> + spin_lock(&kvm->mmu_lock); >> + >> + gfn_start = memslot->base_gfn; >> + gfn_end = memslot->base_gfn + memslot->npages - 1; >> + >> + if (gfn_start >= gfn_end) >> + goto out; > >I don't understand the value of this check here. Are we looking for a >broken memslot? Shouldn't this be a BUG_ON? Is this the place to care >about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e. >2^31. A 64 bit overflow would be caused by a gigantic gfn_start which >would be trouble in many other ways. > >All this to say: please remove the above 5 lines and make code simpler. I will send a patch to cleanup it. Thanks for your review. :) Regards, Wanpeng Li -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Apr 13, 2015 at 10:25 PM, Wanpeng Li <wanpeng.li@linux.intel.com> wrote: > Hi Andres, > On Fri, Apr 10, 2015 at 11:05:26AM -0700, Andres Lagar-Cavilla wrote: > [...] >>> + if (sp->role.direct && >>> + !kvm_is_reserved_pfn(pfn) && >>> + PageTransCompound(pfn_to_page(pfn))) { >> >>Not your fault, but PageTransCompound is very unhappy naming, as it >>also yields true for PageHuge. Suggestion: document this check covers >>static hugetlbfs, or switch to PageCompound() check. >> >>A slightly bolder approach would be to refactor and reuse the nearly >>identical check done in transparent_hugepage_adjust, instead of >>open-coding here. In essence this code is asking for the same check, >>plus the out-of-band check for static hugepages. > > PageCompound() check still return true for both transparent huge pages > and hugetlbfs pages, !PageHuge(page) && PageTransHuge(page) check can > guarantee to catch the right transparent huge pages just as my old commit > e76d30e20be5fc ("mm/hwpoison: fix test for a transparent huge page"). > I will send a patch to fix this. > Why would you want to "fix" it that way? Aren't static hugepages supported? (PageAnon is an inline check and much cheaper than !PageHuge(), which is an actual function call) Please consider my suggestion about refactoring the similar checks in transparent_hugepage_adjust. Thanks a ton Andres >> >> >>> + drop_spte(kvm, sptep); >>> + sptep = rmap_get_first(*rmapp, &iter); >>> + need_tlb_flush = 1; >>> + } else >>> + sptep = rmap_get_next(&iter); >>> + } >>> + >>> + return need_tlb_flush; >>> +} >>> + >>> +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >>> + struct kvm_memory_slot *memslot) >>> +{ >>> + bool flush = false; >>> + unsigned long *rmapp; >>> + unsigned long last_index, index; >>> + gfn_t gfn_start, gfn_end; >>> + >>> + spin_lock(&kvm->mmu_lock); >>> + >>> + gfn_start = memslot->base_gfn; >>> + gfn_end = memslot->base_gfn + memslot->npages - 1; >>> + >>> + if (gfn_start >= gfn_end) >>> + goto out; >> >>I don't understand the value of this check here. Are we looking for a >>broken memslot? Shouldn't this be a BUG_ON? Is this the place to care >>about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e. >>2^31. A 64 bit overflow would be caused by a gigantic gfn_start which >>would be trouble in many other ways. >> >>All this to say: please remove the above 5 lines and make code simpler. > > I will send a patch to cleanup it. Thanks for your review. :) > > Regards, > Wanpeng Li >
On Mon, Apr 13, 2015 at 11:06:25PM -0700, Andres Lagar-Cavilla wrote: >On Mon, Apr 13, 2015 at 10:25 PM, Wanpeng Li <wanpeng.li@linux.intel.com> wrote: >> Hi Andres, >> On Fri, Apr 10, 2015 at 11:05:26AM -0700, Andres Lagar-Cavilla wrote: >> [...] >>>> + if (sp->role.direct && >>>> + !kvm_is_reserved_pfn(pfn) && >>>> + PageTransCompound(pfn_to_page(pfn))) { >>> >>>Not your fault, but PageTransCompound is very unhappy naming, as it >>>also yields true for PageHuge. Suggestion: document this check covers >>>static hugetlbfs, or switch to PageCompound() check. >>> >>>A slightly bolder approach would be to refactor and reuse the nearly >>>identical check done in transparent_hugepage_adjust, instead of >>>open-coding here. In essence this code is asking for the same check, >>>plus the out-of-band check for static hugepages. >> >> PageCompound() check still return true for both transparent huge pages >> and hugetlbfs pages, !PageHuge(page) && PageTransHuge(page) check can >> guarantee to catch the right transparent huge pages just as my old commit >> e76d30e20be5fc ("mm/hwpoison: fix test for a transparent huge page"). >> I will send a patch to fix this. >> >Why would you want to "fix" it that way? Aren't static hugepages supported? > >(PageAnon is an inline check and much cheaper than !PageHuge(), which >is an actual function call) > >Please consider my suggestion about refactoring the similar checks in >transparent_hugepage_adjust. Ok, will do. :) Regards, Wanpeng Li > >Thanks a ton >Andres >>> >>> >>>> + drop_spte(kvm, sptep); >>>> + sptep = rmap_get_first(*rmapp, &iter); >>>> + need_tlb_flush = 1; >>>> + } else >>>> + sptep = rmap_get_next(&iter); >>>> + } >>>> + >>>> + return need_tlb_flush; >>>> +} >>>> + >>>> +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, >>>> + struct kvm_memory_slot *memslot) >>>> +{ >>>> + bool flush = false; >>>> + unsigned long *rmapp; >>>> + unsigned long last_index, index; >>>> + gfn_t gfn_start, gfn_end; >>>> + >>>> + spin_lock(&kvm->mmu_lock); >>>> + >>>> + gfn_start = memslot->base_gfn; >>>> + gfn_end = memslot->base_gfn + memslot->npages - 1; >>>> + >>>> + if (gfn_start >= gfn_end) >>>> + goto out; >>> >>>I don't understand the value of this check here. Are we looking for a >>>broken memslot? Shouldn't this be a BUG_ON? Is this the place to care >>>about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e. >>>2^31. A 64 bit overflow would be caused by a gigantic gfn_start which >>>would be trouble in many other ways. >>> >>>All this to say: please remove the above 5 lines and make code simpler. >> >> I will send a patch to cleanup it. Thanks for your review. :) >> >> Regards, >> Wanpeng Li >> > > > >-- >Andres Lagar-Cavilla | Google Kernel Team | andreslc@google.com -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 30b28dc..91b5bdb 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -854,6 +854,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); void kvm_mmu_slot_remove_write_access(struct kvm *kvm, struct kvm_memory_slot *memslot); +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, + struct kvm_memory_slot *memslot); void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, struct kvm_memory_slot *memslot); void kvm_mmu_slot_largepage_remove_write_access(struct kvm *kvm, diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index cee7592..ba002a0 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4465,6 +4465,79 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, kvm_flush_remote_tlbs(kvm); } +static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, + unsigned long *rmapp) +{ + u64 *sptep; + struct rmap_iterator iter; + int need_tlb_flush = 0; + pfn_t pfn; + struct kvm_mmu_page *sp; + + for (sptep = rmap_get_first(*rmapp, &iter); sptep;) { + BUG_ON(!(*sptep & PT_PRESENT_MASK)); + + sp = page_header(__pa(sptep)); + pfn = spte_to_pfn(*sptep); + + /* + * Lets support EPT only for now, there still needs to figure + * out an efficient way to let these codes be aware what mapping + * level used in guest. + */ + if (sp->role.direct && + !kvm_is_reserved_pfn(pfn) && + PageTransCompound(pfn_to_page(pfn))) { + drop_spte(kvm, sptep); + sptep = rmap_get_first(*rmapp, &iter); + need_tlb_flush = 1; + } else + sptep = rmap_get_next(&iter); + } + + return need_tlb_flush; +} + +void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, + struct kvm_memory_slot *memslot) +{ + bool flush = false; + unsigned long *rmapp; + unsigned long last_index, index; + gfn_t gfn_start, gfn_end; + + spin_lock(&kvm->mmu_lock); + + gfn_start = memslot->base_gfn; + gfn_end = memslot->base_gfn + memslot->npages - 1; + + if (gfn_start >= gfn_end) + goto out; + + rmapp = memslot->arch.rmap[0]; + last_index = gfn_to_index(gfn_end, memslot->base_gfn, + PT_PAGE_TABLE_LEVEL); + + for (index = 0; index <= last_index; ++index, ++rmapp) { + if (*rmapp) + flush |= kvm_mmu_zap_collapsible_spte(kvm, rmapp); + + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { + if (flush) { + kvm_flush_remote_tlbs(kvm); + flush = false; + } + cond_resched_lock(&kvm->mmu_lock); + } + } + + if (flush) + kvm_flush_remote_tlbs(kvm); + +out: + spin_unlock(&kvm->mmu_lock); +} + void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, struct kvm_memory_slot *memslot) { diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 50861dd..a6cd10b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7647,6 +7647,25 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, new = id_to_memslot(kvm->memslots, mem->slot); /* + * Dirty logging tracks sptes in 4k granularity, so large sptes are + * split, the large sptes will be reallocated in the destination + * machine and the guest in the source machine will be destroyed + * when live migration successfully. However, the guest in the source + * machine will continue to run if live migration fail due to some + * reasons, the sptes still keep small which lead to bad performance. + * + * Lazy collapse small sptes into large sptes is intended to handle + * this, the memory region will be scanned on the ioctl context when + * dirty log is stopped, the ones which can be collapsed into large + * pages will be dropped during the scan, it depends the on later #PF + * to reallocate all large sptes. + */ + if ((change != KVM_MR_DELETE) && + (old->flags & KVM_MEM_LOG_DIRTY_PAGES) && + !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) + kvm_mmu_zap_collapsible_sptes(kvm, new); + + /* * Set up write protection and/or dirty logging for the new slot. * * For KVM_MR_DELETE and KVM_MR_MOVE, the shadow pages of old slot have