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

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Date:   Thu, 8 Dec 2022 18:14:01 +1100
From:   Alexey Kardashevskiy <aik@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Venu Busireddy <venu.busireddy@...cle.com>,
        Tony Luck <tony.luck@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Michael Sterritt <sterritt@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH kernel 3/3] x86/sev: Do not handle #VC for DR7 read/write



On 8/12/22 06:07, Sean Christopherson wrote:
> On Wed, Dec 07, 2022, Borislav Petkov wrote:
>> On Thu, Dec 01, 2022 at 05:38:33PM +0000, Sean Christopherson wrote:
>>> Probably high time to add a helper/macro to convert the SEV_STATUS to
>>> the SEV_FEATURES field.
>>
>> Nah, there's a couple of
>>
>> MSR_AMD64_SEV*
>>
>> defines in arch/x86/include/asm/msr-index.h.
>>
>> Bit 5 should simply be added there.
> 
> Ah, yeah, that's much better.

Sorry, I am not following. How is moving the bit makes 
SEV_STATUS_TO_FEATURES() not needed?

When I am setting it in VMSA SEV_FEATURES - it is a bit 5.

Inside a SEV VM, it is SEV_STATUS MSR and there it is bit 7. Mentioned 
MSR_AMD64_SEV* are SEV_STATUS MSR bits.

Since the current patch is bad, I'd rather define the bit twice then:

arch/x86/include/asm/msr-index.h:
#define MSR_AMD64_SEV_FEAT_DEBUG_SWAP    BIT_ULL(7)

arch/x86/include/asm/svm.h
#define SVM_SEV_FEAT_DEBUG_SWAP         BIT(5)

as nothing really says that SEV_FEATURES is always going to be 
SEV_STATUS>>2, even though it is now.

Soooo what is acceptable solution here? Thanks,


-- 
Alexey