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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z4dAXaFM1iWaTjDp@yzhao56-desk.sh.intel.com>
Date: Wed, 15 Jan 2025 12:58:05 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "seanjc@...gle.com" <seanjc@...gle.com>, "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 Wed, Jan 15, 2025 at 06:24:43AM +0800, Edgecombe, Rick P wrote:
> 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.
Hmm, I wouldn't consider this a cleanup, as returning 1 to indicate continuation
of the kernel loop is a well-established convention in arch/x86/kvm.

Returning a positive RET_PF_* in this patch is primarily a preparatory step for
the subsequent patch,
"KVM: TDX: Retry locally in TDX EPT violation handler on RET_PF_RETRY".