linux-kernel - Re: [PATCH 2/7] KVM: x86/mmu: Return RET_PF* instead of 1 in kvm_mmu_page

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Message-ID: <a7b8151808b82550c7c5b5bfba69d334383cb2ba.camel@intel.com>
Date: Tue, 14 Jan 2025 22:24:43 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "seanjc@...gle.com" <seanjc@...gle.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
CC: "Huang, Kai" <kai.huang@...el.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>, "Lindgren,
 Tony" <tony.lindgren@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "dmatlack@...gle.com" <dmatlack@...gle.com>,
	"Hunter, Adrian" <adrian.hunter@...el.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>
Subject: Re: [PATCH 2/7] KVM: x86/mmu: Return RET_PF* instead of 1 in
 kvm_mmu_page_fault()

On Mon, 2025-01-13 at 10:11 +0800, Yan Zhao wrote:
> Return RET_PF* (excluding RET_PF_EMULATE/RET_PF_CONTINUE/RET_PF_INVALID)
> instead of 1 in kvm_mmu_page_fault().
> 
> The callers of kvm_mmu_page_fault() are KVM page fault handlers (i.e.,
> npf_interception(), handle_ept_misconfig(), __vmx_handle_ept_violation(),
> kvm_handle_page_fault()). They either check if the return value is > 0 (as
> in npf_interception()) or pass it further to vcpu_run() to decide whether
> to break out of the kernel loop and return to the user when r <= 0.
> Therefore, returning any positive value is equivalent to returning 1.
> 
> Warn if r == RET_PF_CONTINUE (which should not be a valid value) to ensure
> a positive return value.
> 
> This is a preparation to allow TDX's EPT violation handler to check the
> RET_PF* value and retry internally for RET_PF_RETRY.
> 
> No functional changes are intended.

Any reason why this can't go ahead of the TDX patches? Seems pretty generic
cleanup.