linux-kernel - Re: [PATCH v3 4/6] KVM: MMU: fast invalidate all mmio sptes

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Date:	Thu, 27 Jun 2013 12:21:52 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	avi.kivity@...il.com, mtosatti@...hat.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 4/6] KVM: MMU: fast invalidate all mmio sptes

On Thu, Jun 27, 2013 at 12:14:24PM +0300, Gleb Natapov wrote:
> On Thu, Jun 27, 2013 at 12:01:10PM +0300, Gleb Natapov wrote:
> > On Thu, Jun 27, 2013 at 11:29:00AM +0300, Gleb Natapov wrote:
> > > On Fri, Jun 07, 2013 at 04:51:26PM +0800, Xiao Guangrong wrote:
> > > > This patch tries to introduce a very simple and scale way to invalidate
> > > > all mmio sptes - it need not walk any shadow pages and hold mmu-lock
> > > > 
> > > > 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
> > > > 
> > > So this commit makes Fedora 9 32 bit reboot during boot, Fedora 9 64
> > > fails too, but I haven't checked what happens exactly.
> > > 
> > Something wrong with gfn calculation during mmio:
> > 
> > qemu-system-x86-17003 [000]  3962.625103: handle_mmio_page_fault: addr:c00ba6c0 gfn 100000000ba access a92
> > qemu-system-x86-17003 [000]  3962.774862: handle_mmio_page_fault: addr:ffffb170 gfn 100000fee00 access a92
> > 
> Hmm, so I wounder why get_mmio_spte_gfn() does not clear gen bits.
> 
Hmm, something like patch below fixes it. Will test more.


diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 1fd2c05..aec9c05 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -260,7 +260,8 @@ static bool is_mmio_spte(u64 spte)
 
 static gfn_t get_mmio_spte_gfn(u64 spte)
 {
-	return (spte & ~shadow_mmio_mask) >> PAGE_SHIFT;
+	u64 mask = generation_mmio_spte_mask(MMIO_MAX_GEN) | shadow_mmio_mask;
+	return (spte & ~mask) >> PAGE_SHIFT;
 }
 
 static unsigned get_mmio_spte_access(u64 spte)
--
			Gleb.
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