linux-kernel - Re: [PATCH kernel v3 3/3] x86/sev: Do not handle #VC for DR7 read/write

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Date:   Fri, 20 Jan 2023 21:23:48 +1100
From:   Alexey Kardashevskiy <aik@....com>
To:     "Nikunj A. Dadhania" <nikunj@....com>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Yury Norov <yury.norov@...il.com>,
        Venu Busireddy <venu.busireddy@...cle.com>,
        Tony Luck <tony.luck@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <seanjc@...gle.com>,
        Sandipan Das <sandipan.das@....com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Michael Roth <michael.roth@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Kim Phillips <kim.phillips@....com>,
        Kees Cook <keescook@...omium.org>,
        Juergen Gross <jgross@...e.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Borislav Petkov <bp@...en8.de>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH kernel v3 3/3] x86/sev: Do not handle #VC for DR7
 read/write



On 20/1/23 16:12, Nikunj A. Dadhania wrote:
> On 20/01/23 08:40, Alexey Kardashevskiy wrote:
>> With MSR_AMD64_SEV_DEBUG_SWAP enabled, the VM should not get #VC
>> events for DR7 read/write which it rather avoided.
>>
> 
> SNP guest feature negotiation patch is part of tip now: https://lore.kernel.org/lkml/167414649850.4906.1693185384677559889.tip-bot2@tip-bot2/

Worth mentioning it is tip/x86/urgent (which does not have 
X86_FEATURE_NO_NESTED_DATA_BP), not tip/master (which has 
X86_FEATURE_NO_NESTED_DATA_BP).

> 
> MSR_AMD64_SNP_DEBUG_SWAP is already defined. As this requires guest side changes, please add MSR_AMD64_SNP_DEBUG_SWAP as part of SNP_FEATURES_PRESENT bit mask.

It is MSR_AMD64_SEV_DEBUG_SWAP (SEV, not SNP), it is an SEV-ES thing. 
Why is that feature negotiation SNP-only and not SEV?


-- 
Alexey