From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 16/22] KVM: x86/mmu: remove redundant bits from extended role
Date: Thu, 12 May 2022 15:59:19 +0200 [thread overview]
Message-ID: <e1fc28b6-996f-a436-2664-d6b044d07c82@redhat.com> (raw)
In-Reply-To: <Ynmv2X5eLz2OQDMB@google.com>
On 5/10/22 02:20, Sean Christopherson wrote:
> --
> From: Sean Christopherson<seanjc@google.com>
> Date: Mon, 9 May 2022 17:13:39 -0700
> Subject: [PATCH] KVM: x86/mmu: Return true from is_cr4_pae() iff CR0.PG is set
>
> Condition is_cr4_pae() on is_cr0_pg() in addition to the !4-byte gPTE
> check. From the MMU's perspective, PAE is disabling if paging is
> disabled. The current code works because all callers check is_cr0_pg()
> before invoking is_cr4_pae(), but relying on callers to maintain that
> behavior is unnecessarily risky.
>
> Fixes: faf729621c96 ("KVM: x86/mmu: remove redundant bits from extended role")
> Signed-off-by: Sean Christopherson<seanjc@google.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 909372762363..d1c20170a553 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -240,7 +240,7 @@ static inline bool is_cr0_pg(struct kvm_mmu *mmu)
>
> static inline bool is_cr4_pae(struct kvm_mmu *mmu)
> {
> - return !mmu->cpu_role.base.has_4_byte_gpte;
> + return is_cr0_pg(mmu) && !mmu->cpu_role.base.has_4_byte_gpte;
> }
>
> static struct kvm_mmu_role_regs vcpu_to_role_regs(struct kvm_vcpu *vcpu)
Hmm, thinking more about it this is not needed for two kind of opposite
reasons:
* if is_cr4_pae() really were to represent the raw CR4.PAE value, this
is incorrect and it should be up to the callers to check is_cr0_pg()
* if is_cr4_pae() instead represents 8-byte page table entries, then it
does even before this patch, because of the following logic in
kvm_calc_cpu_role():
if (!____is_cr0_pg(regs)) {
role.base.direct = 1;
return role;
}
...
role.base.has_4_byte_gpte = !____is_cr4_pae(regs);
So whatever meaning we give to is_cr4_pae(), there is no need for the
adjustment.
Paolo
next prev parent reply other threads:[~2022-05-12 13:59 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-14 7:39 [PATCH v3 00/22] https://www.spinics.net/lists/kvm/msg267878.html Paolo Bonzini
2022-04-14 7:39 ` [PATCH 01/22] KVM: x86/mmu: nested EPT cannot be used in SMM Paolo Bonzini
2022-04-14 7:39 ` [PATCH 02/22] KVM: x86/mmu: constify uses of struct kvm_mmu_role_regs Paolo Bonzini
2022-04-14 7:39 ` [PATCH 03/22] KVM: x86/mmu: pull computation of kvm_mmu_role_regs to kvm_init_mmu Paolo Bonzini
2022-04-14 7:39 ` [PATCH 04/22] KVM: x86/mmu: rephrase unclear comment Paolo Bonzini
2022-04-14 7:39 ` [PATCH 05/22] KVM: x86: Clean up and document nested #PF workaround Paolo Bonzini
2022-04-14 7:39 ` [PATCH 06/22] KVM: x86/mmu: remove "bool base_only" arguments Paolo Bonzini
2022-04-14 7:39 ` [PATCH 07/22] KVM: x86/mmu: split cpu_role from mmu_role Paolo Bonzini
2022-04-15 4:16 ` Like Xu
2022-04-14 7:39 ` [PATCH 08/22] KVM: x86/mmu: do not recompute root level from kvm_mmu_role_regs Paolo Bonzini
2022-04-14 7:39 ` [PATCH 09/22] KVM: x86/mmu: remove ept_ad field Paolo Bonzini
2022-04-14 7:39 ` [PATCH 10/22] KVM: x86/mmu: remove kvm_calc_shadow_root_page_role_common Paolo Bonzini
2022-04-14 7:39 ` [PATCH 11/22] KVM: x86/mmu: cleanup computation of MMU roles for two-dimensional paging Paolo Bonzini
2022-04-14 7:39 ` [PATCH 12/22] KVM: x86/mmu: cleanup computation of MMU roles for shadow paging Paolo Bonzini
2022-04-14 7:39 ` [PATCH 13/22] KVM: x86/mmu: store shadow EFER.NX in the MMU role Paolo Bonzini
2022-04-14 7:39 ` [PATCH 14/22] KVM: x86/mmu: remove extended bits from mmu_role, rename field Paolo Bonzini
2022-04-14 7:39 ` [PATCH 15/22] KVM: x86/mmu: rename kvm_mmu_role union Paolo Bonzini
2022-04-14 7:39 ` [PATCH 16/22] KVM: x86/mmu: remove redundant bits from extended role Paolo Bonzini
2022-04-14 8:27 ` Paolo Bonzini
2022-05-10 0:20 ` Sean Christopherson
2022-05-11 13:53 ` Paolo Bonzini
2022-05-12 13:59 ` Paolo Bonzini [this message]
2022-05-12 14:18 ` Sean Christopherson
2022-05-12 16:09 ` Paolo Bonzini
2022-05-12 21:34 ` Sean Christopherson
2022-04-14 7:39 ` [PATCH 17/22] KVM: x86/mmu: remove valid " Paolo Bonzini
2022-04-14 7:39 ` [PATCH 18/22] KVM: x86/mmu: simplify and/or inline computation of shadow MMU roles Paolo Bonzini
2022-04-14 7:39 ` [PATCH 19/22] KVM: x86/mmu: pull CPU mode computation to kvm_init_mmu Paolo Bonzini
2022-04-14 7:39 ` [PATCH 20/22] KVM: x86/mmu: replace shadow_root_level with root_role.level Paolo Bonzini
2022-04-14 7:39 ` [PATCH 21/22] KVM: x86/mmu: replace root_level with cpu_role.base.level Paolo Bonzini
2022-04-14 7:40 ` [PATCH 22/22] KVM: x86/mmu: replace direct_map with root_role.direct Paolo Bonzini
2022-04-14 7:47 ` [PATCH v3 00/22] https://www.spinics.net/lists/kvm/msg267878.html Paolo Bonzini
2022-04-14 15:02 ` Sean Christopherson
2022-04-14 15:09 ` Paolo Bonzini
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