| Message ID | 20210116002100.17339-1-yu.c.zhang@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86/MMU: Do not check unsync status for root SP. | expand |
Hi Paolo, Any comments? Thanks! B.R. Yu On Sat, Jan 16, 2021 at 08:21:00AM +0800, Yu Zhang wrote: > In shadow page table, only leaf SPs may be marked as unsync. > And for non-leaf SPs, we use unsync_children to keep the number > of the unsynced children. In kvm_mmu_sync_root(), sp->unsync > shall always be zero for the root SP, hence no need to check it. > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> > --- > arch/x86/kvm/mmu/mmu.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 6d16481a..1a6bb03 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3412,8 +3412,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) > * mmu_need_write_protect() describe what could go wrong if this > * requirement isn't satisfied. > */ > - if (!smp_load_acquire(&sp->unsync) && > - !smp_load_acquire(&sp->unsync_children)) > + if (!smp_load_acquire(&sp->unsync_children)) > return; > > spin_lock(&vcpu->kvm->mmu_lock); > -- > 1.9.1 >
On Sat, Jan 16, 2021, Yu Zhang wrote: > In shadow page table, only leaf SPs may be marked as unsync. > And for non-leaf SPs, we use unsync_children to keep the number > of the unsynced children. In kvm_mmu_sync_root(), sp->unsync > shall always be zero for the root SP, hence no need to check it. > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> > --- > arch/x86/kvm/mmu/mmu.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 6d16481a..1a6bb03 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3412,8 +3412,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) > * mmu_need_write_protect() describe what could go wrong if this > * requirement isn't satisfied. > */ > - if (!smp_load_acquire(&sp->unsync) && > - !smp_load_acquire(&sp->unsync_children)) > + if (!smp_load_acquire(&sp->unsync_children)) > return; > > spin_lock(&vcpu->kvm->mmu_lock); Looks good. To make this less scary and more obviously correct, maybe move the the WARN on !PG_LEVEL_4K into kvm_unsync_page() instead of having the WARN in its sole caller, and add a WARN in mmu_sync_children()? diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 86af58294272..bc8ee05bb3d3 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -1995,6 +1995,12 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu, LIST_HEAD(invalid_list); bool flush = false; + /* + * Only 4k SPTEs can directly be made unsync, the root shadow page + * should never be unsyc'd. + */ + WARN_ON_ONCE(sp->unsync); + while (mmu_unsync_walk(parent, &pages)) { bool protected = false; @@ -2502,6 +2508,8 @@ EXPORT_SYMBOL_GPL(kvm_mmu_unprotect_page); static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) { + WARN_ON(sp->role.level != PG_LEVEL_4K); + trace_kvm_mmu_unsync_page(sp); ++vcpu->kvm->stat.mmu_unsync; sp->unsync = 1; @@ -2524,7 +2532,6 @@ bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn, if (sp->unsync) continue; - WARN_ON(sp->role.level != PG_LEVEL_4K); kvm_unsync_page(vcpu, sp); } @@ -3406,8 +3413,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) * mmu_need_write_protect() describe what could go wrong if this * requirement isn't satisfied. */ - if (!smp_load_acquire(&sp->unsync) && - !smp_load_acquire(&sp->unsync_children)) + if (!smp_load_acquire(&sp->unsync_children)) return; write_lock(&vcpu->kvm->mmu_lock);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 6d16481a..1a6bb03 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3412,8 +3412,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) * mmu_need_write_protect() describe what could go wrong if this * requirement isn't satisfied. */ - if (!smp_load_acquire(&sp->unsync) && - !smp_load_acquire(&sp->unsync_children)) + if (!smp_load_acquire(&sp->unsync_children)) return; spin_lock(&vcpu->kvm->mmu_lock);
In shadow page table, only leaf SPs may be marked as unsync. And for non-leaf SPs, we use unsync_children to keep the number of the unsynced children. In kvm_mmu_sync_root(), sp->unsync shall always be zero for the root SP, hence no need to check it. Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> --- arch/x86/kvm/mmu/mmu.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)