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Date: Fri, 18 Mar 2022 15:19:34 +0100 From: Thomas Gleixner <tglx@...utronix.de> To: Peter Zijlstra <peterz@...radead.org>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> Cc: mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com, luto@...nel.org, sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com, ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com, hpa@...or.com, jgross@...e.com, jmattson@...gle.com, joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org, pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com, tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com, thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org, linux-kernel@...r.kernel.org, Sean Christopherson <sean.j.christopherson@...el.com>, Dave Hansen <dave.hansen@...ux.intel.com> Subject: Re: [PATCHv6 07/30] x86/traps: Add #VE support for TDX guest On Thu, Mar 17 2022 at 21:21, Peter Zijlstra wrote: > On Thu, Mar 17, 2022 at 08:33:54PM +0300, Kirill A. Shutemov wrote: >> - in NMI entry code (asm_exc_nmi()) before NMI nesting is safe: >> + for NMI from user mode, before switched to thread stack >> + for NMI from kernel, up to end_repead_nmi >> >> After that points #VE is safe. > > In what way is it guaranteed that #VE isn't raised in those places? What > does an auditor / future coder looking to changes things, need to > consider to keep this so. > > From vague memories #VE can be raised on any memop, loading the stack > address in the syscall-gap is a memop. What makes that special? Can we > get a comment _there_ to explain how this is safe such that we can keep > it so? > > Same for the NMI path I suppose. #VE is raised by HLT, CPUID, I/O-Port access, MSR read/write, EPT violations So in the hairy places: - HLT: No business - I/O Ports: That would be outright stupid to use - CPUID: Should never be used - Emphasis on should :) - MSRs: Same as CPUID - EPT: Well.... Thanks, Thomas
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