| Message ID | 20140218172247.ca61f503.yoshikawa_takuya_b1@lab.ntt.co.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 02/18/2014 04:22 PM, Takuya Yoshikawa wrote: > When this was introduced, kvm_flush_remote_tlbs() could be called > without holding mmu_lock. It is now acknowledged that the function > must be called before releasing mmu_lock, and all callers have already > been changed to do so. > I have already posted the patch to moving flush tlb out of mmu-lock when do dirty tracking: KVM: MMU: flush tlb out of mmu lock when write-protect the sptes Actually some patches (patch 1 - patch 4) in that patchset can be pickup-ed separately and i should apologize for the patchset was not updated for a long time since i was busy on other development. And moving tlb flush out of mmu-lock should be going on in the future, so i think the B patch is more acceptable. -- 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
(2014/02/18 18:43), Xiao Guangrong wrote: > On 02/18/2014 04:22 PM, Takuya Yoshikawa wrote: >> When this was introduced, kvm_flush_remote_tlbs() could be called >> without holding mmu_lock. It is now acknowledged that the function >> must be called before releasing mmu_lock, and all callers have already >> been changed to do so. >> > > I have already posted the patch to moving flush tlb out of mmu-lock > when do dirty tracking: > KVM: MMU: flush tlb out of mmu lock when write-protect the sptes Yes, I had your patch in mind, so made patch B. > > Actually some patches (patch 1 - patch 4) in that patchset can be > pickup-ed separately and i should apologize for the patchset was > not updated for a long time since i was busy on other development. Looking forward to seeing that work again! > > And moving tlb flush out of mmu-lock should be going on in the > future, so i think the B patch is more acceptable. > Maybe. Some time ago, someone working on non-x86 stuff asked us why smp_mb() and cmpxchg() were used there. So a brief comment which points them to the note on sync_page() will be helpful. 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
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index cba218a..b1e6c1b 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -913,7 +913,8 @@ static gpa_t FNAME(gva_to_gpa_nested)(struct kvm_vcpu *vcpu, gva_t vaddr, * and kvm_mmu_notifier_invalidate_range_start detect the mapping page isn't * used by guest then tlbs are not flushed, so guest is allowed to access the * freed pages. - * And we increase kvm->tlbs_dirty to delay tlbs flush in this case. + * We set tlbs_dirty to let the notifier know this change and delay the flush + * until such a case actually happens. */ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) { @@ -942,7 +943,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) return -EINVAL; if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) { - vcpu->kvm->tlbs_dirty++; + vcpu->kvm->tlbs_dirty = true; continue; } @@ -957,7 +958,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) if (gfn != sp->gfns[i]) { drop_spte(vcpu->kvm, &sp->spt[i]); - vcpu->kvm->tlbs_dirty++; + vcpu->kvm->tlbs_dirty = true; continue; } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index f5937b8..ed1cc89 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -401,7 +401,7 @@ struct kvm { unsigned long mmu_notifier_seq; long mmu_notifier_count; #endif - long tlbs_dirty; + bool tlbs_dirty; struct list_head devices; }; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index a9e999a..51744da 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -186,12 +186,15 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req) void kvm_flush_remote_tlbs(struct kvm *kvm) { - long dirty_count = kvm->tlbs_dirty; - - smp_mb(); if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH)) ++kvm->stat.remote_tlb_flush; - cmpxchg(&kvm->tlbs_dirty, dirty_count, 0); + /* + * tlbs_dirty is used only for optimizing x86's shadow paging code with + * mmu notifiers in mind, see the note on sync_page(). Since it is + * always protected with mmu_lock there, should kvm_flush_remote_tlbs() + * be called before releasing mmu_lock, this is safe. + */ + kvm->tlbs_dirty = false; } EXPORT_SYMBOL_GPL(kvm_flush_remote_tlbs);
When this was introduced, kvm_flush_remote_tlbs() could be called without holding mmu_lock. It is now acknowledged that the function must be called before releasing mmu_lock, and all callers have already been changed to do so. There is no need to use smp_mb() and cmpxchg() any more. Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> --- arch/x86/kvm/paging_tmpl.h | 7 ++++--- include/linux/kvm_host.h | 2 +- virt/kvm/kvm_main.c | 11 +++++++---- 3 files changed, 12 insertions(+), 8 deletions(-)