linux-kernel - Re: [PATCH] KVM: VMX: fix tlb flush with invalid root

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Message-Id: <201007050852.49001.sheng@linux.intel.com>
Date:	Mon, 5 Jul 2010 08:52:48 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	kvm@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: VMX: fix tlb flush with invalid root

On Saturday 03 July 2010 16:02:42 Xiao Guangrong wrote:
> Commit 341d9b535b6c simplify reload logic while entry guest mode, it
> can avoid unnecessary sync-root if KVM_REQ_MMU_RELOAD and
> KVM_REQ_MMU_SYNC both set.

Which commit you are talking about? Can't find 341d9b535b6c...

--
regards
Yang, Sheng

> 
> But, it cause a issue that when we handle 'KVM_REQ_TLB_FLUSH', the
> root is invalid, it is triggered during my test:
> 
> Kernel BUG at ffffffffa00212b8 [verbose debug info unavailable]
> ......
> 
>  [<ffffffff810f5caf>] ? fget_light+0x111/0x28e
>  [<ffffffff81103963>] sys_ioctl+0x47/0x6a
>  [<ffffffff81002c1b>] system_call_fastpath+0x16/0x1b
> Code: f0 eb 21 f7 c2 00 00 00 04 74 22 48 8d 45 f0 48 c7 45 f0 00 00 00 00
> 48 c7 45 f8 00 00 00 00 b9 02 00 00 00 66 0f 38 80 08 77 02 <0f> 0b c9 c3
> 55 48 89 e5 0f 1f 44 00 00 ba 00 68 00 00 48 8b 8f RIP 
> [<ffffffffa00212b8>] vmx_flush_tlb+0xdf/0xe3 [kvm_intel]
>  RSP <ffff8800be269ca8>
> 
> Fixed by directly return if the root is not ready.
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
>  arch/x86/include/asm/kvm_host.h |    2 ++
>  arch/x86/kvm/mmu.c              |    2 --
>  arch/x86/kvm/vmx.c              |    5 ++++-
>  3 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h
> b/arch/x86/include/asm/kvm_host.h index 2bda624..8f522ec 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -40,6 +40,8 @@
>  				  0xFFFFFF0000000000ULL)
> 
>  #define INVALID_PAGE (~(hpa_t)0)
> +#define VALID_PAGE(x) ((x) != INVALID_PAGE)
> +
>  #define UNMAPPED_GVA (~(gpa_t)0)
> 
>  /* KVM Hugepage definitions for x86 */
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index a0c5c31..399ddb0 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -92,8 +92,6 @@ module_param(oos_shadow, bool, 0644);
>  #define PT_FIRST_AVAIL_BITS_SHIFT 9
>  #define PT64_SECOND_AVAIL_BITS_SHIFT 52
> 
> -#define VALID_PAGE(x) ((x) != INVALID_PAGE)
> -
>  #define PT64_LEVEL_BITS 9
> 
>  #define PT64_LEVEL_SHIFT(level) \
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 806ab12..ebaaeaf 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1831,8 +1831,11 @@ static void exit_lmode(struct kvm_vcpu *vcpu)
>  static void vmx_flush_tlb(struct kvm_vcpu *vcpu)
>  {
>  	vpid_sync_context(to_vmx(vcpu));
> -	if (enable_ept)
> +	if (enable_ept) {
> +		if (!VALID_PAGE(vcpu->arch.mmu.root_hpa))
> +			return;
>  		ept_sync_context(construct_eptp(vcpu->arch.mmu.root_hpa));
> +	}
>  }
> 
>  static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu)
--
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