From: David Matlack <dmatlack@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
seanjc@google.com, vkuznets@redhat.com
Subject: Re: [PATCH 01/23] KVM: MMU: pass uses_nx directly to reset_shadow_zero_bits_mask
Date: Fri, 4 Feb 2022 17:59:47 +0000 [thread overview]
Message-ID: <Yf1pk1EEBXj0O0/p@google.com> (raw)
In-Reply-To: <20220204115718.14934-2-pbonzini@redhat.com>
On Fri, Feb 04, 2022 at 06:56:56AM -0500, Paolo Bonzini wrote:
> reset_shadow_zero_bits_mask has a very unintuitive way of deciding
> whether the shadow pages will use the NX bit. The function is used in
> two cases, shadow paging and shadow NPT; shadow paging has a use for
> EFER.NX and needs to force it enabled, while shadow NPT only needs it
> depending on L1's setting.
>
> The actual root problem here is that is_efer_nx, despite being part
> of the "base" role, only matches the format of the shadow pages in the
> NPT case. For now, just remove the ugly variable initialization and move
> the call to reset_shadow_zero_bits_mask out of shadow_mmu_init_context.
> The parameter can then be removed after the root problem in the role
> is fixed.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: David Matlack <dmatlack@google.com>
(I agree this commit makes no functional change.)
> ---
> arch/x86/kvm/mmu/mmu.c | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 296f8723f9ae..9424ae90f1ef 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4410,18 +4410,9 @@ static inline u64 reserved_hpa_bits(void)
> * follow the features in guest.
> */
> static void reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu,
> - struct kvm_mmu *context)
> + struct kvm_mmu *context,
> + bool uses_nx)
> {
> - /*
> - * KVM uses NX when TDP is disabled to handle a variety of scenarios,
> - * notably for huge SPTEs if iTLB multi-hit mitigation is enabled and
> - * to generate correct permissions for CR0.WP=0/CR4.SMEP=1/EFER.NX=0.
> - * The iTLB multi-hit workaround can be toggled at any time, so assume
> - * NX can be used by any non-nested shadow MMU to avoid having to reset
> - * MMU contexts. Note, KVM forces EFER.NX=1 when TDP is disabled.
> - */
> - bool uses_nx = is_efer_nx(context) || !tdp_enabled;
> -
> /* @amd adds a check on bit of SPTEs, which KVM shouldn't use anyways. */
> bool is_amd = true;
> /* KVM doesn't use 2-level page tables for the shadow MMU. */
> @@ -4829,8 +4820,6 @@ static void shadow_mmu_init_context(struct kvm_vcpu *vcpu, struct kvm_mmu *conte
>
> reset_guest_paging_metadata(vcpu, context);
> context->shadow_root_level = new_role.base.level;
> -
> - reset_shadow_zero_bits_mask(vcpu, context);
> }
>
> static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu,
> @@ -4841,6 +4830,16 @@ static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu,
> kvm_calc_shadow_mmu_root_page_role(vcpu, regs, false);
>
> shadow_mmu_init_context(vcpu, context, regs, new_role);
> +
> + /*
> + * KVM uses NX when TDP is disabled to handle a variety of scenarios,
> + * notably for huge SPTEs if iTLB multi-hit mitigation is enabled and
> + * to generate correct permissions for CR0.WP=0/CR4.SMEP=1/EFER.NX=0.
> + * The iTLB multi-hit workaround can be toggled at any time, so assume
> + * NX can be used by any non-nested shadow MMU to avoid having to reset
> + * MMU contexts. Note, KVM forces EFER.NX=1 when TDP is disabled.
> + */
> + reset_shadow_zero_bits_mask(vcpu, context, true);
> }
>
> static union kvm_mmu_role
> @@ -4872,6 +4871,7 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
> __kvm_mmu_new_pgd(vcpu, nested_cr3, new_role.base);
>
> shadow_mmu_init_context(vcpu, context, ®s, new_role);
> + reset_shadow_zero_bits_mask(vcpu, context, is_efer_nx(context));
Out of curiousity, how does KVM mitigate iTLB multi-hit when shadowing
NPT and the guest has not enabled EFER.NX?
> }
> EXPORT_SYMBOL_GPL(kvm_init_shadow_npt_mmu);
>
> --
> 2.31.1
>
>
next prev parent reply other threads:[~2022-02-04 17:59 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-04 11:56 [PATCH 00/23] KVM: MMU: MMU role refactoring Paolo Bonzini
2022-02-04 11:56 ` [PATCH 01/23] KVM: MMU: pass uses_nx directly to reset_shadow_zero_bits_mask Paolo Bonzini
2022-02-04 17:59 ` David Matlack [this message]
2022-02-05 14:52 ` Paolo Bonzini
2022-02-07 16:09 ` Sean Christopherson
2022-02-07 21:50 ` David Matlack
2022-02-10 0:30 ` Sean Christopherson
2022-02-10 16:38 ` Paolo Bonzini
2022-02-04 11:56 ` [PATCH 02/23] KVM: MMU: nested EPT cannot be used in SMM Paolo Bonzini
2022-02-04 18:16 ` David Matlack
2022-02-09 22:43 ` Sean Christopherson
2022-02-04 11:56 ` [PATCH 03/23] KVM: MMU: remove valid from extended role Paolo Bonzini
2022-02-04 18:32 ` David Matlack
2022-02-05 14:50 ` Paolo Bonzini
2022-02-09 22:54 ` Sean Christopherson
2022-02-10 9:53 ` Paolo Bonzini
2022-02-04 11:56 ` [PATCH 04/23] KVM: MMU: constify uses of struct kvm_mmu_role_regs Paolo Bonzini
2022-02-04 18:41 ` David Matlack
2022-02-09 22:57 ` Sean Christopherson
2022-02-04 11:57 ` [PATCH 05/23] KVM: MMU: pull computation of kvm_mmu_role_regs to kvm_init_mmu Paolo Bonzini
2022-02-04 18:45 ` David Matlack
2022-02-04 11:57 ` [PATCH 06/23] KVM: MMU: load new PGD once nested two-dimensional paging is initialized Paolo Bonzini
2022-02-04 19:18 ` David Matlack
2022-02-07 13:50 ` Paolo Bonzini
2022-02-07 14:35 ` Paolo Bonzini
2022-02-09 12:34 ` Paolo Bonzini
2022-02-04 11:57 ` [PATCH 07/23] KVM: MMU: remove kvm_mmu_calc_root_page_role Paolo Bonzini
2022-02-04 19:32 ` David Matlack
2022-02-05 14:46 ` Paolo Bonzini
2022-02-10 0:47 ` Sean Christopherson
2022-02-10 9:52 ` Paolo Bonzini
2022-02-10 17:29 ` Sean Christopherson
2022-02-10 17:43 ` Paolo Bonzini
2022-02-04 11:57 ` [PATCH 08/23] KVM: MMU: rephrase unclear comment Paolo Bonzini
2022-02-04 19:38 ` David Matlack
2022-02-04 11:57 ` [PATCH 09/23] KVM: MMU: remove "bool base_only" arguments Paolo Bonzini
2022-02-04 19:41 ` David Matlack
2022-02-04 11:57 ` [PATCH 10/23] KVM: MMU: split cpu_role from mmu_role Paolo Bonzini
2022-02-04 21:57 ` David Matlack
2022-02-05 14:49 ` Paolo Bonzini
2022-02-07 21:38 ` David Matlack
2022-02-04 11:57 ` [PATCH 11/23] KVM: MMU: do not recompute root level from kvm_mmu_role_regs Paolo Bonzini
2022-02-07 22:10 ` David Matlack
2022-02-07 22:17 ` David Matlack
2022-02-04 11:57 ` [PATCH 12/23] KVM: MMU: remove ept_ad field Paolo Bonzini
2022-02-04 11:57 ` [PATCH 13/23] KVM: MMU: remove kvm_calc_shadow_root_page_role_common Paolo Bonzini
2022-02-07 22:25 ` David Matlack
2022-02-04 11:57 ` [PATCH 14/23] KVM: MMU: cleanup computation of MMU roles for two-dimensional paging Paolo Bonzini
2022-02-04 11:57 ` [PATCH 15/23] KVM: MMU: cleanup computation of MMU roles for shadow paging Paolo Bonzini
2022-02-04 11:57 ` [PATCH 16/23] KVM: MMU: remove extended bits from mmu_role Paolo Bonzini
2022-02-04 11:57 ` [PATCH 17/23] KVM: MMU: remove redundant bits from extended role Paolo Bonzini
2022-02-04 11:57 ` [PATCH 18/23] KVM: MMU: fetch shadow EFER.NX from MMU role Paolo Bonzini
2022-02-04 11:57 ` [PATCH 19/23] KVM: MMU: simplify and/or inline computation of shadow MMU roles Paolo Bonzini
2022-02-04 11:57 ` [PATCH 20/23] KVM: MMU: pull CPU role computation to kvm_init_mmu Paolo Bonzini
2022-02-07 22:42 ` David Matlack
2022-02-04 11:57 ` [PATCH 21/23] KVM: MMU: store shadow_root_level into mmu_role Paolo Bonzini
2022-02-07 23:00 ` David Matlack
2022-02-04 11:57 ` [PATCH 22/23] KVM: MMU: use cpu_role for root_level Paolo Bonzini
2022-02-07 23:01 ` David Matlack
2022-02-04 11:57 ` [PATCH 23/23] KVM: MMU: replace direct_map with mmu_role.direct Paolo Bonzini
2022-02-07 23:02 ` David Matlack
2022-02-07 23:08 ` [PATCH 00/23] KVM: MMU: MMU role refactoring David Matlack
2022-02-07 23:27 ` Sean Christopherson
2022-02-07 23:53 ` David Matlack
2022-02-10 1:11 ` Sean Christopherson
2022-02-10 11:58 ` Paolo Bonzini
2022-02-10 16:55 ` Sean Christopherson
2022-02-10 17:30 ` Paolo Bonzini
2022-02-10 19:28 ` Sean Christopherson
2022-02-09 22:31 ` Sean Christopherson
2022-02-10 9:54 ` Paolo Bonzini
2022-02-14 18:14 ` David Matlack
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