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Message-ID: <ccf85ef8-049b-40a9-adcb-eac0cdc57b37@intel.com>
Date: Thu, 7 Mar 2024 13:11:15 +1300
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH 12/16] KVM: x86/mmu: Move slot checks from
 __kvm_faultin_pfn() to kvm_faultin_pfn()
Content-Language: en-US
To: Sean Christopherson <seanjc@google.com>, Paolo Bonzini
	<pbonzini@redhat.com>
CC: <kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>, Yan Zhao
	<yan.y.zhao@intel.com>, Isaku Yamahata <isaku.yamahata@intel.com>, "Michael
 Roth" <michael.roth@amd.com>, Yu Zhang <yu.c.zhang@linux.intel.com>, "Chao
 Peng" <chao.p.peng@linux.intel.com>, Fuad Tabba <tabba@google.com>, "David
 Matlack" <dmatlack@google.com>
References: <20240228024147.41573-1-seanjc@google.com>
 <20240228024147.41573-13-seanjc@google.com>
From: "Huang, Kai" <kai.huang@intel.com>
In-Reply-To: <20240228024147.41573-13-seanjc@google.com>
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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@google.com>

Feel free to add:

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