linux-kernel - Re: [PATCH 12/16] KVM: x86/mmu: Move slot checks from __kvm_faultin_pfn() to kvm_faultin

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Date: Thu, 7 Mar 2024 13:11:15 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
	<pbonzini@...hat.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Yan Zhao
	<yan.y.zhao@...el.com>, Isaku Yamahata <isaku.yamahata@...el.com>, "Michael
 Roth" <michael.roth@....com>, Yu Zhang <yu.c.zhang@...ux.intel.com>, "Chao
 Peng" <chao.p.peng@...ux.intel.com>, Fuad Tabba <tabba@...gle.com>, "David
 Matlack" <dmatlack@...gle.com>
Subject: Re: [PATCH 12/16] KVM: x86/mmu: Move slot checks from
 __kvm_faultin_pfn() to kvm_faultin_pfn()




Ditto for accesses to KVM internal memslots from L2, which
> KVM also treats as emulated MMIO.

Nit:

This is not accurate anymore due to your previous patch ("KVM: x86/mmu: 
Don't force emulation of L2 accesses to non-APIC internal slots").

> 
> 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>

Feel free to add:

Reviewed-by: Kai Huang <kai.huang@...el.com>