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Date: Mon, 10 Jun 2013 16:39:37 +0800
From: Xiao Guangrong <xiaoguangrong.eric@...il.com>
To: Gleb Natapov <gleb@...hat.com>
CC: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
avi.kivity@...il.com, mtosatti@...hat.com, pbonzini@...hat.com,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 0/6] KVM: MMU: fast invalidate all mmio sptes
On 06/10/2013 03:56 PM, Gleb Natapov wrote:
> On Fri, Jun 07, 2013 at 04:51:22PM +0800, Xiao Guangrong wrote:
>> Changelog:
>> V3:
>> All of these changes are from Gleb's review:
>> 1) rename RET_MMIO_PF_EMU to RET_MMIO_PF_EMULATE.
>> 2) smartly adjust kvm generation number in kvm_current_mmio_generatio()
>> to avoid kvm_memslots->generation overflow.
>>
>> V2:
>> - rename kvm_mmu_invalid_mmio_spte to kvm_mmu_invalid_mmio_sptes
>> - use kvm->memslots->generation as kvm global generation-number
>> - fix comment and codestyle
>> - init kvm generation close to mmio wrap-around value
>> - keep kvm_mmu_zap_mmio_sptes
>>
>> The current way is holding hot mmu-lock and walking all shadow pages, this
>> is not scale. This patchset tries to introduce a very simple and scale way
>> to fast invalidate all mmio sptes - it need not walk any shadow pages and hold
>> any locks.
>>
>> The idea is simple:
>> KVM maintains a global mmio valid generation-number which is stored in
>> kvm->memslots.generation and every mmio spte stores the current global
>> generation-number into his available bits when it is created
>>
>> When KVM need zap all mmio sptes, it just simply increase the global
>> generation-number. When guests do mmio access, KVM intercepts a MMIO #PF
>> then it walks the shadow page table and get the mmio spte. If the
>> generation-number on the spte does not equal the global generation-number,
>> it will go to the normal #PF handler to update the mmio spte
>>
>> Since 19 bits are used to store generation-number on mmio spte, we zap all
>> mmio sptes when the number is round
>>
> Looks good to me, but doesn't tis obsolete kvm_mmu_zap_mmio_sptes() and
> sp->mmio_cached, so they should be removed as part of the patch series?
Yes, i agree, they should be removed. :)
There is the patch to do these things:
>From bc1bc36e2640059f06c4860af802ecc74e1f3d2d Mon Sep 17 00:00:00 2001
From: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Date: Mon, 10 Jun 2013 16:28:55 +0800
Subject: [PATCH 7/6] KVM: MMU: drop kvm_mmu_zap_mmio_sptes
Drop kvm_mmu_zap_mmio_sptes and use kvm_mmu_invalidate_zap_all_pages
instead to handle mmio generation number overflow
Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/mmu.c | 22 +---------------------
2 files changed, 1 insertion(+), 22 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 90d05ed..966f265 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -230,7 +230,6 @@ struct kvm_mmu_page {
#endif
int write_flooding_count;
- bool mmio_cached;
};
struct kvm_pio_request {
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 35cd0b6..c87b19d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -246,13 +246,11 @@ static unsigned int kvm_current_mmio_generation(struct kvm *kvm)
static void mark_mmio_spte(struct kvm *kvm, u64 *sptep, u64 gfn,
unsigned access)
{
- struct kvm_mmu_page *sp = page_header(__pa(sptep));
unsigned int gen = kvm_current_mmio_generation(kvm);
u64 mask = generation_mmio_spte_mask(gen);
access &= ACC_WRITE_MASK | ACC_USER_MASK;
mask |= shadow_mmio_mask | access | gfn << PAGE_SHIFT;
- sp->mmio_cached = true;
trace_mark_mmio_spte(sptep, gfn, access, gen);
mmu_spte_set(sptep, mask);
@@ -4362,24 +4360,6 @@ void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm)
spin_unlock(&kvm->mmu_lock);
}
-static void kvm_mmu_zap_mmio_sptes(struct kvm *kvm)
-{
- struct kvm_mmu_page *sp, *node;
- LIST_HEAD(invalid_list);
-
- spin_lock(&kvm->mmu_lock);
-restart:
- list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
- if (!sp->mmio_cached)
- continue;
- if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list))
- goto restart;
- }
-
- kvm_mmu_commit_zap_page(kvm, &invalid_list);
- spin_unlock(&kvm->mmu_lock);
-}
-
static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
{
return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages));
@@ -4395,7 +4375,7 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm)
* when mark memslot invalid.
*/
if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1)))
- kvm_mmu_zap_mmio_sptes(kvm);
+ kvm_mmu_invalidate_zap_all_pages(kvm);
}
static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc)
--
1.8.1.4
--
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