Re: [PATCH v3 6/6] KVM: MMU: delay flush all tlbs on sync_page path
On Mon, Nov 22, 2010 at 11:45:18AM +0800, Xiao Guangrong wrote:
On 11/20/2010 12:11 AM, Marcelo Tosatti wrote:
void kvm_flush_remote_tlbs(struct kvm *kvm)
{
+ int dirty_count = atomic_read(kvm-tlbs_dirty);
+
+ smp_mb();
if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
++kvm-stat.remote_tlb_flush;
+ atomic_sub(dirty_count, kvm-tlbs_dirty);
}
This is racy because kvm_flush_remote_tlbs might be called without
mmu_lock protection.
Sorry for my carelessness, it should be 'cmpxchg' here.
You could decrease the counter on
invalidate_page/invalidate_range_start only,
I want to avoid a unnecessary tlbs flush, if tlbs have been flushed
after sync_page, then we don't need flush tlbs on invalidate_page/
invalidate_range_start path.
these are not fast paths
anyway.
How about below patch? it just needs one atomic operation.
---
arch/x86/kvm/paging_tmpl.h |4 ++--
include/linux/kvm_host.h |2 ++
virt/kvm/kvm_main.c|7 ++-
3 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index dfb906f..e64192f 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -781,14 +781,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp)
gfn = gpte_to_gfn(gpte);
if (FNAME(map_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 4bd663d..dafd90e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -249,6 +249,7 @@ struct kvm {
struct mmu_notifier mmu_notifier;
unsigned long mmu_notifier_seq;
long mmu_notifier_count;
+ long tlbs_dirty;
#endif
};
@@ -377,6 +378,7 @@ 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..fe0a1a7 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)
{
+ 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);
}
Still problematic, if tlbs_dirty is set in the point indicated above.
Invalidate page should be quite rare, so checking for tlb_dirty only
there is OK.
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Re: [PATCH v3 6/6] KVM: MMU: delay flush all tlbs on sync_page path
On Mon, Nov 22, 2010 at 12:19:25PM -0200, Marcelo Tosatti wrote:
On Mon, Nov 22, 2010 at 11:45:18AM +0800, Xiao Guangrong wrote:
On 11/20/2010 12:11 AM, Marcelo Tosatti wrote:
void kvm_flush_remote_tlbs(struct kvm *kvm)
{
+int dirty_count = atomic_read(kvm-tlbs_dirty);
+
+smp_mb();
if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
++kvm-stat.remote_tlb_flush;
+atomic_sub(dirty_count, kvm-tlbs_dirty);
}
This is racy because kvm_flush_remote_tlbs might be called without
mmu_lock protection.
Sorry for my carelessness, it should be 'cmpxchg' here.
You could decrease the counter on
invalidate_page/invalidate_range_start only,
I want to avoid a unnecessary tlbs flush, if tlbs have been flushed
after sync_page, then we don't need flush tlbs on invalidate_page/
invalidate_range_start path.
these are not fast paths
anyway.
How about below patch? it just needs one atomic operation.
---
arch/x86/kvm/paging_tmpl.h |4 ++--
include/linux/kvm_host.h |2 ++
virt/kvm/kvm_main.c|7 ++-
3 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index dfb906f..e64192f 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -781,14 +781,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp)
gfn = gpte_to_gfn(gpte);
if (FNAME(map_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 4bd663d..dafd90e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -249,6 +249,7 @@ struct kvm {
struct mmu_notifier mmu_notifier;
unsigned long mmu_notifier_seq;
long mmu_notifier_count;
+ long tlbs_dirty;
#endif
};
@@ -377,6 +378,7 @@ 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..fe0a1a7 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)
{
+ 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);
}
Still problematic, if tlbs_dirty is set in the point indicated above.
Invalidate page should be quite rare, so checking for tlb_dirty only
there is OK.
My bad, the patch is fine.
--
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the body of a message to majord...@vger.kernel.org
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Re: [PATCH v3 6/6] KVM: MMU: delay flush all tlbs on sync_page path
On 11/20/2010 12:11 AM, Marcelo Tosatti wrote:
void kvm_flush_remote_tlbs(struct kvm *kvm)
{
+int dirty_count = atomic_read(kvm-tlbs_dirty);
+
+smp_mb();
if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
++kvm-stat.remote_tlb_flush;
+atomic_sub(dirty_count, kvm-tlbs_dirty);
}
This is racy because kvm_flush_remote_tlbs might be called without
mmu_lock protection.
Sorry for my carelessness, it should be 'cmpxchg' here.
You could decrease the counter on
invalidate_page/invalidate_range_start only,
I want to avoid a unnecessary tlbs flush, if tlbs have been flushed
after sync_page, then we don't need flush tlbs on invalidate_page/
invalidate_range_start path.
these are not fast paths
anyway.
How about below patch? it just needs one atomic operation.
---
arch/x86/kvm/paging_tmpl.h |4 ++--
include/linux/kvm_host.h |2 ++
virt/kvm/kvm_main.c|7 ++-
3 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index dfb906f..e64192f 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -781,14 +781,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct
kvm_mmu_page *sp)
gfn = gpte_to_gfn(gpte);
if (FNAME(map_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 4bd663d..dafd90e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -249,6 +249,7 @@ struct kvm {
struct mmu_notifier mmu_notifier;
unsigned long mmu_notifier_seq;
long mmu_notifier_count;
+ long tlbs_dirty;
#endif
};
@@ -377,6 +378,7 @@ 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..fe0a1a7 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)
{
+ 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);
}
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
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Re: [PATCH v3 6/6] KVM: MMU: delay flush all tlbs on sync_page path
On Fri, Nov 19, 2010 at 05:05:38PM +0800, Xiao Guangrong wrote:
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 xiaoguangr...@cn.fujitsu.com
---
arch/x86/kvm/paging_tmpl.h |4 ++--
include/linux/kvm_host.h |7 +++
virt/kvm/kvm_main.c|8 +++-
3 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index dfb906f..d5c302a 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -781,14 +781,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp)
gfn = gpte_to_gfn(gpte);
if (FNAME(map_invalid_gpte)(vcpu, sp, sp-spt[i], gpte)) {
- kvm_flush_remote_tlbs(vcpu-kvm);
+ kvm_mark_tlbs_dirty(vcpu-kvm);
continue;
}
if (gfn != sp-gfns[i]) {
drop_spte(vcpu-kvm, sp-spt[i],
shadow_trap_nonpresent_pte);
- kvm_flush_remote_tlbs(vcpu-kvm);
+ kvm_mark_tlbs_dirty(vcpu-kvm);
continue;
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4bd663d..82d449b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -249,6 +249,7 @@ struct kvm {
struct mmu_notifier mmu_notifier;
unsigned long mmu_notifier_seq;
long mmu_notifier_count;
+ atomic_t tlbs_dirty;
#endif
};
@@ -377,6 +378,12 @@ 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);
+
+static inline void kvm_mark_tlbs_dirty(struct kvm *kvm)
+{
+ atomic_inc(kvm-tlbs_dirty);
+}
+
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..2962569 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 = atomic_read(kvm-tlbs_dirty);
+
+ smp_mb();
if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
++kvm-stat.remote_tlb_flush;
+ atomic_sub(dirty_count, kvm-tlbs_dirty);
}
This is racy because kvm_flush_remote_tlbs might be called without
mmu_lock protection. You could decrease the counter on
invalidate_page/invalidate_range_start only, these are not fast paths
anyway.
void kvm_reload_remote_mmus(struct kvm *kvm)
@@ -249,7 +253,8 @@ 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) |
+ atomic_read(kvm-tlbs_dirty);
spin_unlock(kvm-mmu_lock);
srcu_read_unlock(kvm-srcu, idx);
@@ -293,6 +298,7 @@ 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 |= atomic_read(kvm-tlbs_dirty);
spin_unlock(kvm-mmu_lock);
srcu_read_unlock(kvm-srcu, idx);
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