linux-kernel - Re: [PATCH 13/17] KVM: x86/mmu: Move slot checks from __kvm_faultin_pfn() to kvm_faultin

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Date: Mon, 13 May 2024 14:27:31 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>, Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCH 13/17] KVM: x86/mmu: Move slot checks from
 __kvm_faultin_pfn() to kvm_faultin_pfn()

On 5/7/2024 11:58 PM, Paolo Bonzini wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> Move the checks related to the validity of an access to a memslot from the
> inner __kvm_faultin_pfn() to its sole caller, kvm_faultin_pfn().  This
> allows emulating accesses to the APIC access page, which don't need to
> resolve a pfn, even if there is a relevant in-progress mmu_notifier
> invalidation.  Ditto for accesses to KVM internal memslots from L2, which
> KVM also treats as emulated MMIO.
> 
> More importantly, this will allow for future cleanup by having the
> "no memslot" case bail from kvm_faultin_pfn() very early on.
> 
> Go to rather extreme and gross lengths to make the change a glorified
> nop, e.g. call into __kvm_faultin_pfn() even when there is no slot, as the
> related code is very subtle.  E.g. fault->slot can be nullified if it
> points at the APIC access page, some flows in KVM x86 expect fault->pfn
> to be KVM_PFN_NOSLOT, while others check only fault->slot, etc.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Reviewed-by: Kai Huang <kai.huang@...el.com>
> Message-ID: <20240228024147.41573-13-seanjc@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>