| Message ID | 20130703171804.89d6cc2c.yoshikawa_takuya_b1@lab.ntt.co.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto: > Since kvm_arch_prepare_memory_region() is called right after installing > the slot marked invalid, wraparound checking should be there to avoid > zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. > > Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> > --- > This seems to be the simplest solution for fixing the off-by-one issue > we discussed before. > > arch/x86/kvm/mmu.c | 5 +---- > arch/x86/kvm/x86.c | 7 +++++++ > 2 files changed, 8 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 0d094da..bf7af1e 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) > /* > * The very rare case: if the generation-number is round, > * zap all shadow pages. > - * > - * The max value is MMIO_MAX_GEN - 1 since it is not called > - * when mark memslot invalid. > */ > - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { > + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { > printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n"); > kvm_mmu_invalidate_zap_all_pages(kvm); > } > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 7d71c0f..9ddd4ff 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > memslot->userspace_addr = userspace_addr; > } > > + /* > + * In these cases, slots->generation has been increased for marking the > + * slot invalid, so we need wraparound checking here. > + */ > + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) > + kvm_mmu_invalidate_mmio_sptes(kvm); > + > return 0; > } > > Applied, thanks. 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 07/03/2013 04:28 PM, Paolo Bonzini wrote: > Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto: >> Since kvm_arch_prepare_memory_region() is called right after installing >> the slot marked invalid, wraparound checking should be there to avoid >> zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. >> >> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> >> --- >> This seems to be the simplest solution for fixing the off-by-one issue >> we discussed before. >> >> arch/x86/kvm/mmu.c | 5 +---- >> arch/x86/kvm/x86.c | 7 +++++++ >> 2 files changed, 8 insertions(+), 4 deletions(-) >> >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index 0d094da..bf7af1e 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) >> /* >> * The very rare case: if the generation-number is round, >> * zap all shadow pages. >> - * >> - * The max value is MMIO_MAX_GEN - 1 since it is not called >> - * when mark memslot invalid. >> */ >> - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { >> + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { >> printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n"); >> kvm_mmu_invalidate_zap_all_pages(kvm); >> } >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 7d71c0f..9ddd4ff 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, >> memslot->userspace_addr = userspace_addr; >> } >> >> + /* >> + * In these cases, slots->generation has been increased for marking the >> + * slot invalid, so we need wraparound checking here. >> + */ >> + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) >> + kvm_mmu_invalidate_mmio_sptes(kvm); >> + >> return 0; >> } >> >> > > Applied, thanks. Please wait a while. I can not understand it very clearly. This conditional check will cause caching a overflow value into mmio spte. The simple case is that kvm adds new slots for many times, the mmio-gen is easily more than MMIO_MAX_GEN. -- 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 Wed, 03 Jul 2013 16:39:25 +0800 Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> wrote: > Please wait a while. I can not understand it very clearly. > > This conditional check will cause caching a overflow value into mmio spte. > The simple case is that kvm adds new slots for many times, the mmio-gen is easily > more than MMIO_MAX_GEN. Unconditional checking in commit_memory_region() is still there to treat such cases. Takuya -- 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
Il 03/07/2013 10:39, Xiao Guangrong ha scritto: > On 07/03/2013 04:28 PM, Paolo Bonzini wrote: >> Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto: >>> Since kvm_arch_prepare_memory_region() is called right after installing >>> the slot marked invalid, wraparound checking should be there to avoid >>> zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. >>> >>> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> >>> --- >>> This seems to be the simplest solution for fixing the off-by-one issue >>> we discussed before. >>> >>> arch/x86/kvm/mmu.c | 5 +---- >>> arch/x86/kvm/x86.c | 7 +++++++ >>> 2 files changed, 8 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>> index 0d094da..bf7af1e 100644 >>> --- a/arch/x86/kvm/mmu.c >>> +++ b/arch/x86/kvm/mmu.c >>> @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) >>> /* >>> * The very rare case: if the generation-number is round, >>> * zap all shadow pages. >>> - * >>> - * The max value is MMIO_MAX_GEN - 1 since it is not called >>> - * when mark memslot invalid. >>> */ >>> - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { >>> + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { >>> printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n"); >>> kvm_mmu_invalidate_zap_all_pages(kvm); >>> } >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>> index 7d71c0f..9ddd4ff 100644 >>> --- a/arch/x86/kvm/x86.c >>> +++ b/arch/x86/kvm/x86.c >>> @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, >>> memslot->userspace_addr = userspace_addr; >>> } >>> >>> + /* >>> + * In these cases, slots->generation has been increased for marking the >>> + * slot invalid, so we need wraparound checking here. >>> + */ >>> + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) >>> + kvm_mmu_invalidate_mmio_sptes(kvm); >>> + >>> return 0; >>> } >>> >>> >> >> Applied, thanks. > > Please wait a while. I can not understand it very clearly. I'm only applying to queue anyway until Linus pulls. > This conditional check will cause caching a overflow value into mmio spte. > The simple case is that kvm adds new slots for many times, the mmio-gen is easily > more than MMIO_MAX_GEN. The mmio generation is masked to MMIO_GEN_MASK: return (kvm_memslots(kvm)->generation + MMIO_MAX_GEN - 150) & MMIO_GEN_MASK; What Takuya's patch does is basically "if __kvm_set_memory_region called install_new_memslots, call kvm_mmu_invalidate_mmio_sptes". kvm_arch_prepare_memory_region is preceded by install_new_memslots if change is KVM_MR_DELETE or KVM_MR_MOVE. kvm_arch_commit_memory_region is always preceded by install_new_memslots. So the logic in x86.c matches the one in __kvm_set_memory_region. With this change, each change to the regions is matched by a call to kvm_mmu_invalidate_mmio_sptes, and there is no need to invalidate twice before wraparound. 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 07/03/2013 04:50 PM, Takuya Yoshikawa wrote: > On Wed, 03 Jul 2013 16:39:25 +0800 > Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> wrote: > >> Please wait a while. I can not understand it very clearly. >> >> This conditional check will cause caching a overflow value into mmio spte. >> The simple case is that kvm adds new slots for many times, the mmio-gen is easily >> more than MMIO_MAX_GEN. > > Unconditional checking in commit_memory_region() is still there > to treat such cases. WHY? -- 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 07/03/2013 04:39 PM, Xiao Guangrong wrote: > On 07/03/2013 04:28 PM, Paolo Bonzini wrote: >> Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto: >>> Since kvm_arch_prepare_memory_region() is called right after installing >>> the slot marked invalid, wraparound checking should be there to avoid >>> zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. >>> >>> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> >>> --- >>> This seems to be the simplest solution for fixing the off-by-one issue >>> we discussed before. >>> >>> arch/x86/kvm/mmu.c | 5 +---- >>> arch/x86/kvm/x86.c | 7 +++++++ >>> 2 files changed, 8 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>> index 0d094da..bf7af1e 100644 >>> --- a/arch/x86/kvm/mmu.c >>> +++ b/arch/x86/kvm/mmu.c >>> @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) >>> /* >>> * The very rare case: if the generation-number is round, >>> * zap all shadow pages. >>> - * >>> - * The max value is MMIO_MAX_GEN - 1 since it is not called >>> - * when mark memslot invalid. >>> */ >>> - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { >>> + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { >>> printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n"); >>> kvm_mmu_invalidate_zap_all_pages(kvm); >>> } >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>> index 7d71c0f..9ddd4ff 100644 >>> --- a/arch/x86/kvm/x86.c >>> +++ b/arch/x86/kvm/x86.c >>> @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, >>> memslot->userspace_addr = userspace_addr; >>> } >>> >>> + /* >>> + * In these cases, slots->generation has been increased for marking the >>> + * slot invalid, so we need wraparound checking here. >>> + */ >>> + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) >>> + kvm_mmu_invalidate_mmio_sptes(kvm); >>> + >>> return 0; >>> } >>> >>> >> >> Applied, thanks. > > Please wait a while. I can not understand it very clearly. > > This conditional check will cause caching a overflow value into mmio spte. > The simple case is that kvm adds new slots for many times, the mmio-gen is easily > more than MMIO_MAX_GEN. > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to the end of install_new_memslots(). -- 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 Wed, Jul 03, 2013 at 04:50:36PM +0800, Xiao Guangrong wrote: > On 07/03/2013 04:39 PM, Xiao Guangrong wrote: > > On 07/03/2013 04:28 PM, Paolo Bonzini wrote: > >> Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto: > >>> Since kvm_arch_prepare_memory_region() is called right after installing > >>> the slot marked invalid, wraparound checking should be there to avoid > >>> zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. > >>> > >>> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> > >>> --- > >>> This seems to be the simplest solution for fixing the off-by-one issue > >>> we discussed before. > >>> > >>> arch/x86/kvm/mmu.c | 5 +---- > >>> arch/x86/kvm/x86.c | 7 +++++++ > >>> 2 files changed, 8 insertions(+), 4 deletions(-) > >>> > >>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > >>> index 0d094da..bf7af1e 100644 > >>> --- a/arch/x86/kvm/mmu.c > >>> +++ b/arch/x86/kvm/mmu.c > >>> @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) > >>> /* > >>> * The very rare case: if the generation-number is round, > >>> * zap all shadow pages. > >>> - * > >>> - * The max value is MMIO_MAX_GEN - 1 since it is not called > >>> - * when mark memslot invalid. > >>> */ > >>> - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { > >>> + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { > >>> printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n"); > >>> kvm_mmu_invalidate_zap_all_pages(kvm); > >>> } > >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > >>> index 7d71c0f..9ddd4ff 100644 > >>> --- a/arch/x86/kvm/x86.c > >>> +++ b/arch/x86/kvm/x86.c > >>> @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > >>> memslot->userspace_addr = userspace_addr; > >>> } > >>> > >>> + /* > >>> + * In these cases, slots->generation has been increased for marking the > >>> + * slot invalid, so we need wraparound checking here. > >>> + */ > >>> + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) > >>> + kvm_mmu_invalidate_mmio_sptes(kvm); > >>> + > >>> return 0; > >>> } > >>> > >>> > >> > >> Applied, thanks. > > > > Please wait a while. I can not understand it very clearly. > > > > This conditional check will cause caching a overflow value into mmio spte. > > The simple case is that kvm adds new slots for many times, the mmio-gen is easily > > more than MMIO_MAX_GEN. > > > > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to > the end of install_new_memslots(). > Exactly. Why should we hide it in obscure functions? -- Gleb. -- 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
Il 03/07/2013 10:50, Xiao Guangrong ha scritto: >> > Please wait a while. I can not understand it very clearly. >> > >> > This conditional check will cause caching a overflow value into mmio spte. >> > The simple case is that kvm adds new slots for many times, the mmio-gen is easily >> > more than MMIO_MAX_GEN. >> > > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to > the end of install_new_memslots(). > > Yes, the actual operation would be the same as this patch. You can rename kvm_mmu_invalidate_mmio_sptes to kvm_arch_memslots_installed, or something like that. But it would have to touch all architectures. 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
Il 03/07/2013 10:53, Gleb Natapov ha scritto: >>> > > Please wait a while. I can not understand it very clearly. >>> > > >>> > > This conditional check will cause caching a overflow value into mmio spte. >>> > > The simple case is that kvm adds new slots for many times, the mmio-gen is easily >>> > > more than MMIO_MAX_GEN. >>> > > >> > >> > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to >> > the end of install_new_memslots(). >> > > Exactly. Why should we hide it in obscure functions? Because kvm_mmu_invalidate_mmio_sptes is an x86-specific function, and we already have a good arch API to hook into __kvm_set_memory_region. Another possible implementation is to cache the last memslot generation, check it in kvm_arch_prepare/commit_memory_region, and call kvm_mmu_invalidate_mmio_sptes if it changed. This would avoid the need to keep "((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE))" in sync between the two places. But I don't think it is a substantial improvement. 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 07/03/2013 04:50 PM, Paolo Bonzini wrote: > Il 03/07/2013 10:39, Xiao Guangrong ha scritto: >> On 07/03/2013 04:28 PM, Paolo Bonzini wrote: >>> Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto: >>>> Since kvm_arch_prepare_memory_region() is called right after installing >>>> the slot marked invalid, wraparound checking should be there to avoid >>>> zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. >>>> >>>> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> >>>> --- >>>> This seems to be the simplest solution for fixing the off-by-one issue >>>> we discussed before. >>>> >>>> arch/x86/kvm/mmu.c | 5 +---- >>>> arch/x86/kvm/x86.c | 7 +++++++ >>>> 2 files changed, 8 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>>> index 0d094da..bf7af1e 100644 >>>> --- a/arch/x86/kvm/mmu.c >>>> +++ b/arch/x86/kvm/mmu.c >>>> @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) >>>> /* >>>> * The very rare case: if the generation-number is round, >>>> * zap all shadow pages. >>>> - * >>>> - * The max value is MMIO_MAX_GEN - 1 since it is not called >>>> - * when mark memslot invalid. >>>> */ >>>> - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { >>>> + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { >>>> printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n"); >>>> kvm_mmu_invalidate_zap_all_pages(kvm); >>>> } >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>> index 7d71c0f..9ddd4ff 100644 >>>> --- a/arch/x86/kvm/x86.c >>>> +++ b/arch/x86/kvm/x86.c >>>> @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, >>>> memslot->userspace_addr = userspace_addr; >>>> } >>>> >>>> + /* >>>> + * In these cases, slots->generation has been increased for marking the >>>> + * slot invalid, so we need wraparound checking here. >>>> + */ >>>> + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) >>>> + kvm_mmu_invalidate_mmio_sptes(kvm); >>>> + >>>> return 0; >>>> } >>>> >>>> >>> >>> Applied, thanks. >> >> Please wait a while. I can not understand it very clearly. > > I'm only applying to queue anyway until Linus pulls. Okay. :) > >> This conditional check will cause caching a overflow value into mmio spte. >> The simple case is that kvm adds new slots for many times, the mmio-gen is easily >> more than MMIO_MAX_GEN. > > The mmio generation is masked to MMIO_GEN_MASK: > > return (kvm_memslots(kvm)->generation + > MMIO_MAX_GEN - 150) & MMIO_GEN_MASK; > > What Takuya's patch does is basically "if __kvm_set_memory_region called > install_new_memslots, call kvm_mmu_invalidate_mmio_sptes". > > kvm_arch_prepare_memory_region is preceded by install_new_memslots if > change is KVM_MR_DELETE or KVM_MR_MOVE. kvm_arch_commit_memory_region > is always preceded by install_new_memslots. So the logic in x86.c > matches the one in __kvm_set_memory_region. > > With this change, each change to the regions is matched by a call to > kvm_mmu_invalidate_mmio_sptes, and there is no need to invalidate twice > before wraparound. Oh. My mistake, i did not noticed that the check in kvm_arch_commit_memory_region() is still there. The change is okay to work. But, the check in two places seems unclean. :( -- 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 Wed, Jul 03, 2013 at 10:57:35AM +0200, Paolo Bonzini wrote: > Il 03/07/2013 10:53, Gleb Natapov ha scritto: > >>> > > Please wait a while. I can not understand it very clearly. > >>> > > > >>> > > This conditional check will cause caching a overflow value into mmio spte. > >>> > > The simple case is that kvm adds new slots for many times, the mmio-gen is easily > >>> > > more than MMIO_MAX_GEN. > >>> > > > >> > > >> > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to > >> > the end of install_new_memslots(). > >> > > > Exactly. Why should we hide it in obscure functions? > > Because kvm_mmu_invalidate_mmio_sptes is an x86-specific function, and > we already have a good arch API to hook into __kvm_set_memory_region. > From this patch it can be seen that the API is not good enough. Generation update API is missing. > Another possible implementation is to cache the last memslot generation, > check it in kvm_arch_prepare/commit_memory_region, and call > kvm_mmu_invalidate_mmio_sptes if it changed. This would avoid the need > to keep "((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE))" in sync > between the two places. But I don't think it is a substantial improvement. > Why are you trying to overcome API shortcomings instead of fixing the API. -- Gleb. -- 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 Wed, 03 Jul 2013 10:53:51 +0200 Paolo Bonzini <pbonzini@redhat.com> wrote: > Il 03/07/2013 10:50, Xiao Guangrong ha scritto: > >> > Please wait a while. I can not understand it very clearly. > >> > > >> > This conditional check will cause caching a overflow value into mmio spte. > >> > The simple case is that kvm adds new slots for many times, the mmio-gen is easily > >> > more than MMIO_MAX_GEN. > >> > > > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to > > the end of install_new_memslots(). > > > > > > Yes, the actual operation would be the same as this patch. You can > rename kvm_mmu_invalidate_mmio_sptes to kvm_arch_memslots_installed, or > something like that. But it would have to touch all architectures. I tried to avoid introducing x86-centric code into the generic one. If another arch can gain something by such function, I'm willing to touch all arch code. Takuya -- 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 Wed, Jul 03, 2013 at 06:05:00PM +0900, Takuya Yoshikawa wrote: > On Wed, 03 Jul 2013 10:53:51 +0200 > Paolo Bonzini <pbonzini@redhat.com> wrote: > > > Il 03/07/2013 10:50, Xiao Guangrong ha scritto: > > >> > Please wait a while. I can not understand it very clearly. > > >> > > > >> > This conditional check will cause caching a overflow value into mmio spte. > > >> > The simple case is that kvm adds new slots for many times, the mmio-gen is easily > > >> > more than MMIO_MAX_GEN. > > >> > > > > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to > > > the end of install_new_memslots(). > > > > > > > > > > Yes, the actual operation would be the same as this patch. You can > > rename kvm_mmu_invalidate_mmio_sptes to kvm_arch_memslots_installed, or > > something like that. But it would have to touch all architectures. > > I tried to avoid introducing x86-centric code into the generic one. > > If another arch can gain something by such function, I'm willing to > touch all arch code. > Please do. X86 is the most optimized one so it does things other arches do not yet. Slot generation update hook sounds generic enough. -- Gleb. -- 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
Il 03/07/2013 11:05, Gleb Natapov ha scritto: >>> Yes, the actual operation would be the same as this patch. You can >>> rename kvm_mmu_invalidate_mmio_sptes to kvm_arch_memslots_installed, or >>> something like that. But it would have to touch all architectures. >> >> I tried to avoid introducing x86-centric code into the generic one. >> >> If another arch can gain something by such function, I'm willing to >> touch all arch code. >> > Please do. X86 is the most optimized one so it does things other arches > do not yet. Slot generation update hook sounds generic enough. Yes, makes sense. However, this patch is still an improvement because the current code is too easily mistaken for an off-by-one bug. Any improvements to the API can go on top. 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 Wed, Jul 03, 2013 at 11:08:18AM +0200, Paolo Bonzini wrote: > Il 03/07/2013 11:05, Gleb Natapov ha scritto: > >>> Yes, the actual operation would be the same as this patch. You can > >>> rename kvm_mmu_invalidate_mmio_sptes to kvm_arch_memslots_installed, or > >>> something like that. But it would have to touch all architectures. > >> > >> I tried to avoid introducing x86-centric code into the generic one. > >> > >> If another arch can gain something by such function, I'm willing to > >> touch all arch code. > >> > > Please do. X86 is the most optimized one so it does things other arches > > do not yet. Slot generation update hook sounds generic enough. > > Yes, makes sense. However, this patch is still an improvement because > the current code is too easily mistaken for an off-by-one bug. > > Any improvements to the API can go on top. > If Takuya will send the proper fix shortly I do not see any reason to apply this one. It does not fix any bug. -- Gleb. -- 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 Wed, 3 Jul 2013 12:10:57 +0300 Gleb Natapov <gleb@redhat.com> wrote: > > Yes, makes sense. However, this patch is still an improvement because > > the current code is too easily mistaken for an off-by-one bug. > > > > Any improvements to the API can go on top. > > > If Takuya will send the proper fix shortly I do not see any reason to > apply this one. It does not fix any bug. No problem. Please give me a day or so. Thank you everyone for revewing this patch! Takuya -- 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
Il 03/07/2013 11:10, Gleb Natapov ha scritto: > On Wed, Jul 03, 2013 at 11:08:18AM +0200, Paolo Bonzini wrote: >> Il 03/07/2013 11:05, Gleb Natapov ha scritto: >>>>> Yes, the actual operation would be the same as this patch. You can >>>>> rename kvm_mmu_invalidate_mmio_sptes to kvm_arch_memslots_installed, or >>>>> something like that. But it would have to touch all architectures. >>>> >>>> I tried to avoid introducing x86-centric code into the generic one. >>>> >>>> If another arch can gain something by such function, I'm willing to >>>> touch all arch code. >>>> >>> Please do. X86 is the most optimized one so it does things other arches >>> do not yet. Slot generation update hook sounds generic enough. >> >> Yes, makes sense. However, this patch is still an improvement because >> the current code is too easily mistaken for an off-by-one bug. >> >> Any improvements to the API can go on top. >> > If Takuya will send the proper fix shortly I do not see any reason to > apply this one. It does not fix any bug. It is still a small bug to do two zaps when only one is needed... 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
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 0d094da..bf7af1e 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) /* * The very rare case: if the generation-number is round, * zap all shadow pages. - * - * The max value is MMIO_MAX_GEN - 1 since it is not called - * when mark memslot invalid. */ - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n"); kvm_mmu_invalidate_zap_all_pages(kvm); } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 7d71c0f..9ddd4ff 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, memslot->userspace_addr = userspace_addr; } + /* + * In these cases, slots->generation has been increased for marking the + * slot invalid, so we need wraparound checking here. + */ + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) + kvm_mmu_invalidate_mmio_sptes(kvm); + return 0; }
Since kvm_arch_prepare_memory_region() is called right after installing the slot marked invalid, wraparound checking should be there to avoid zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> --- This seems to be the simplest solution for fixing the off-by-one issue we discussed before. arch/x86/kvm/mmu.c | 5 +---- arch/x86/kvm/x86.c | 7 +++++++ 2 files changed, 8 insertions(+), 4 deletions(-)