From: Avi Kivity <avi@redhat.com>
To: Sheng Yang <sheng@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>, kvm@vger.kernel.org
Subject: Re: [PATCH 4/4] VMX: x86: Only reset MMU when necessary
Date: Wed, 12 May 2010 09:59:14 +0300 [thread overview]
Message-ID: <4BEA51C2.5000708@redhat.com> (raw)
In-Reply-To: <1273645986-21526-4-git-send-email-sheng@linux.intel.com>
On 05/12/2010 09:33 AM, Sheng Yang wrote:
> Only modifying some bits of CR0/CR4 needs paging mode switch.
>
> Add update_rsvd_bits_mask() to address EFER.NX bit updating for reserved bits.
>
>
> @@ -2335,6 +2335,19 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, int level)
> }
> }
>
> +void update_rsvd_bits_mask(struct kvm_vcpu *vcpu)
> +{
> + if (!is_paging(vcpu))
> + return;
> + if (is_long_mode(vcpu))
> + reset_rsvds_bits_mask(vcpu, PT64_ROOT_LEVEL);
> + else if (is_pae(vcpu))
> + reset_rsvds_bits_mask(vcpu, PT32E_ROOT_LEVEL);
> + else
> + reset_rsvds_bits_mask(vcpu, PT32_ROOT_LEVEL);
> +}
> +EXPORT_SYMBOL_GPL(update_rsvd_bits_mask);
>
Needs a kvm_ prefix if made a global symbol. But isn't nx switching
rare enough so we can reload the mmu completely?
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b59fc67..971a295 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -416,6 +416,10 @@ out:
>
> static int __kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
> {
> + unsigned long old_cr0 = kvm_read_cr0(vcpu);
> + unsigned long update_bits = X86_CR0_PG | X86_CR0_PE |
> + X86_CR0_CD | X86_CR0_NW;
>
PE doesn't affect paging, CD, NW don't either?
What about WP?
> +
> cr0 |= X86_CR0_ET;
>
> #ifdef CONFIG_X86_64
> @@ -449,7 +453,8 @@ static int __kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>
> kvm_x86_ops->set_cr0(vcpu, cr0);
>
> - kvm_mmu_reset_context(vcpu);
> + if ((cr0 ^ old_cr0)& update_bits)
> + kvm_mmu_reset_context(vcpu);
> return 0;
> }
>
>
> @@ -692,6 +698,8 @@ static u32 emulated_msrs[] = {
>
> static int set_efer(struct kvm_vcpu *vcpu, u64 efer)
> {
> + u64 old_efer = vcpu->arch.efer;
> +
> if (efer& efer_reserved_bits)
> return 1;
>
> @@ -722,6 +730,9 @@ static int set_efer(struct kvm_vcpu *vcpu, u64 efer)
>
> vcpu->arch.mmu.base_role.nxe = (efer& EFER_NX)&& !tdp_enabled;
>
> + if ((efer ^ old_efer)& EFER_NX)
> + update_rsvd_bits_mask(vcpu);
> +
> return 0;
> }
>
I think it's fine to reset the entire mmu context here, most guests
won't toggle nx all the time. But it needs to be in patch 3, otherwise
we have a regression between 3 and 4.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
next prev parent reply other threads:[~2010-05-12 6:59 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-11 5:30 [PATCH 1/4] KVM: x86: Check LMA bit before set_efer Sheng Yang
2010-05-11 5:30 ` [PATCH 2/4] KVM: Clean up duplicate assignment Sheng Yang
2010-05-11 5:30 ` [PATCH 3/4] KVM: x86: Remove kvm_mmu_reset_context() in kvm_set_efer() Sheng Yang
2010-05-11 19:33 ` Marcelo Tosatti
2010-05-11 5:30 ` [PATCH 4/4] VMX: x86: Only reset MMU when necessary Sheng Yang
2010-05-11 19:36 ` Marcelo Tosatti
2010-05-12 1:53 ` Sheng Yang
2010-05-12 2:09 ` Sheng Yang
2010-05-12 6:31 ` Avi Kivity
2010-05-12 6:33 ` [PATCH 1/4] KVM: x86: Check LMA bit before set_efer Sheng Yang
2010-05-12 6:33 ` [PATCH 2/4] KVM: Clean up duplicate assignment Sheng Yang
2010-05-12 6:33 ` [PATCH 3/4] KVM: x86: Remove kvm_mmu_reset_context() in kvm_set_efer() Sheng Yang
2010-05-12 6:33 ` [PATCH 4/4] VMX: x86: Only reset MMU when necessary Sheng Yang
2010-05-12 6:59 ` Avi Kivity [this message]
2010-05-12 7:31 ` Sheng Yang
2010-05-12 8:11 ` Avi Kivity
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