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 18:09:49 +0200 [thread overview]
Message-ID: <8c92f44f-3e56-5a5d-76c2-b50b8fe58b3d@redhat.com> (raw)
In-Reply-To: <Yn0XNnqnbstGSiEl@google.com>
On 5/12/22 16:18, Sean Christopherson wrote:
> On Thu, May 12, 2022, Paolo Bonzini wrote:
>> 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.
>
> I disagree, because is_cr4_pae() doesn't represent either of those things. It
> represents the effective (not raw) CR4.PAE from the MMU's perspective.
Doh, you're right that has_4_byte_gpte is actually 0 if CR0.PG=0.
Swapping stuff back is hard.
What do you think about a WARN_ON_ONCE(!is_cr0_pg(mmu))?
Paolo
next prev parent reply other threads:[~2022-05-12 16:09 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
2022-05-12 14:18 ` Sean Christopherson
2022-05-12 16:09 ` Paolo Bonzini [this message]
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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