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Message-ID: <4D7999E6.9000406@cn.fujitsu.com>
Date: Fri, 11 Mar 2011 11:41:26 +0800
From: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To: Avi Kivity <avi@...hat.com>
CC: Marcelo Tosatti <mtosatti@...hat.com>,
LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] KVM: MMU: cleanup pte write path
On 03/10/2011 06:21 PM, Avi Kivity wrote:
> On 03/09/2011 09:43 AM, Xiao Guangrong wrote:
>> This patch does:
>> - call vcpu->arch.mmu.update_pte directly
>> - use gfn_to_pfn_atomic in update_pte path
>>
>> The suggestion is from Avi.
>>
>>
>>
>> - mmu_guess_page_from_pte_write(vcpu, gpa, gentry);
>> + mmu_seq = vcpu->kvm->mmu_notifier_seq;
>> + smp_rmb();
>
> smp_rmb() should come before, no? but the problem was present in the original code, too.
>
Um, i think smb_rmb is used to avoid read mmu_notifier_seq reorder to the
behind of gfn_to_pfn in the original code, like this:
CPU A: B
gfn_to_pfn
invalidate_page
mmu_notifier_seq++
read mmu_notifier_seq
then, cpu A will get the invalid pfn.
But, after this cleanup patch, we use gfn_to_pfn_atomic in the protection
of mmu_lock, so i think the mmu_seq code can be removed.
Subject: [PATCH] KVM: MMU: remove mmu_seq verification in kvm_mmu_pte_write
The mmu_seq verification can be removed since we get the pfn in the
protection of mmu_lock
Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/mmu.c | 16 +++++-----------
arch/x86/kvm/paging_tmpl.h | 4 +---
3 files changed, 7 insertions(+), 15 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index c8af099..18a95e9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -256,7 +256,7 @@ struct kvm_mmu {
struct kvm_mmu_page *sp);
void (*invlpg)(struct kvm_vcpu *vcpu, gva_t gva);
void (*update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
- u64 *spte, const void *pte, unsigned long mmu_seq);
+ u64 *spte, const void *pte);
hpa_t root_hpa;
int root_level;
int shadow_root_level;
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 22fae75..2841805 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1206,7 +1206,7 @@ static void nonpaging_invlpg(struct kvm_vcpu *vcpu, gva_t gva)
static void nonpaging_update_pte(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp, u64 *spte,
- const void *pte, unsigned long mmu_seq)
+ const void *pte)
{
WARN_ON(1);
}
@@ -3163,9 +3163,8 @@ static void mmu_pte_write_zap_pte(struct kvm_vcpu *vcpu,
}
static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu,
- struct kvm_mmu_page *sp,
- u64 *spte,
- const void *new, unsigned long mmu_seq)
+ struct kvm_mmu_page *sp, u64 *spte,
+ const void *new)
{
if (sp->role.level != PT_PAGE_TABLE_LEVEL) {
++vcpu->kvm->stat.mmu_pde_zapped;
@@ -3173,7 +3172,7 @@ static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu,
}
++vcpu->kvm->stat.mmu_pte_updated;
- vcpu->arch.mmu.update_pte(vcpu, sp, spte, new, mmu_seq);
+ vcpu->arch.mmu.update_pte(vcpu, sp, spte, new);
}
static bool need_remote_flush(u64 old, u64 new)
@@ -3229,7 +3228,6 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
struct kvm_mmu_page *sp;
struct hlist_node *node;
LIST_HEAD(invalid_list);
- unsigned long mmu_seq;
u64 entry, gentry, *spte;
unsigned pte_size, page_offset, misaligned, quadrant, offset;
int level, npte, invlpg_counter, r, flooded = 0;
@@ -3271,9 +3269,6 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
break;
}
- mmu_seq = vcpu->kvm->mmu_notifier_seq;
- smp_rmb();
-
spin_lock(&vcpu->kvm->mmu_lock);
if (atomic_read(&vcpu->kvm->arch.invlpg_counter) != invlpg_counter)
gentry = 0;
@@ -3345,8 +3340,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
if (gentry &&
!((sp->role.word ^ vcpu->arch.mmu.base_role.word)
& mask.word))
- mmu_pte_write_new_pte(vcpu, sp, spte, &gentry,
- mmu_seq);
+ mmu_pte_write_new_pte(vcpu, sp, spte, &gentry);
if (!remote_flush && need_remote_flush(entry, *spte))
remote_flush = true;
++spte;
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 7514050..3dee563 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -325,7 +325,7 @@ no_present:
}
static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
- u64 *spte, const void *pte, unsigned long mmu_seq)
+ u64 *spte, const void *pte)
{
pt_element_t gpte;
unsigned pte_access;
@@ -342,8 +342,6 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
kvm_release_pfn_clean(pfn);
return;
}
- if (mmu_notifier_retry(vcpu, mmu_seq))
- return;
/*
* we call mmu_set_spte() with host_writable = true beacuse that
--
1.7.4
--
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