Re: [PATCH v3 6/6] KVM: MMU: delay flush all tlbs on sync_page path

Xiao Guangrong
2010-11-23T03:13:00Z

On 11/23/2010 05:46 AM, Marcelo Tosatti wrote:

>
> My bad, the patch is fine.
>

Post the path with appropriate format and add some comments.

Subject: [PATCH v3 6/6] KVM: MMU: delay flush all tlbs on sync_page path
From: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>

Quote from Avi:
| I don't think we need to flush immediately; set a "tlb dirty" bit somewhere
| that is cleareded when we flush the tlb. kvm_mmu_notifier_invalidate_page()
| can consult the bit and force a flush if set.

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
arch/x86/kvm/paging_tmpl.h | 12 ++++++++++--
include/linux/kvm_host.h | 2 ++
virt/kvm/kvm_main.c | 7 ++++++-
3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index a43f4cc..2b3d66c 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -746,6 +746,14 @@ static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
* Using the cached information from sp->gfns is safe because:
* - The spte has a reference to the struct page, so the pfn for a given gfn
* can't change unless all sptes pointing to it are nuked first.
+ *
+ * Note:
+ * We should flush all tlbs if spte is dropped even though guest is
+ * responsible for it. Since if we don't, kvm_mmu_notifier_invalidate_page
+ * 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.
*/
static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
{
@@ -781,14 +789,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
gfn = gpte_to_gfn(gpte);

if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) {
- kvm_flush_remote_tlbs(vcpu->kvm);
+ vcpu->kvm->tlbs_dirty++;
continue;
}

if (gfn != sp->gfns[i]) {
drop_spte(vcpu->kvm, &sp->spt[i],
shadow_trap_nonpresent_pte);
- kvm_flush_remote_tlbs(vcpu->kvm);
+ vcpu->kvm->tlbs_dirty++;
continue;
}

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f17beae..96a5e0b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -254,6 +254,7 @@ struct kvm {
struct mmu_notifier mmu_notifier;
unsigned long mmu_notifier_seq;
long mmu_notifier_count;
+ long tlbs_dirty;
#endif
};

@@ -382,6 +383,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
void kvm_resched(struct kvm_vcpu *vcpu);
void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
+
void kvm_flush_remote_tlbs(struct kvm *kvm);
void kvm_reload_remote_mmus(struct kvm *kvm);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fb93ff9..c4ee364 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -168,8 +168,12 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)

void kvm_flush_remote_tlbs(struct kvm *kvm)
{
+ int 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);
}

void kvm_reload_remote_mmus(struct kvm *kvm)
@@ -249,7 +253,7 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
idx = srcu_read_lock(&kvm->srcu);
spin_lock(&kvm->mmu_lock);
kvm->mmu_notifier_seq++;
- need_tlb_flush = kvm_unmap_hva(kvm, address);
+ need_tlb_flush = kvm_unmap_hva(kvm, address) | kvm->tlbs_dirty;
spin_unlock(&kvm->mmu_lock);
srcu_read_unlock(&kvm->srcu, idx);

@@ -293,6 +297,7 @@ static void kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
kvm->mmu_notifier_count++;
for (; start < end; start += PAGE_SIZE)
need_tlb_flush |= kvm_unmap_hva(kvm, start);
+ need_tlb_flush |= kvm->tlbs_dirty;
spin_unlock(&kvm->mmu_lock);
srcu_read_unlock(&kvm->srcu, idx);

--
1.7.0.4