linux-kernel - Re: [PATCH kernel v2 2/3] KVM: SEV: Enable data breakpoints in SEV-ES

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Message-ID: <50e9a5df-b574-5fa5-466e-7bed48523897@amd.com>
Date:   Thu, 12 Jan 2023 08:32:46 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>, Alexey Kardashevskiy <aik@....com>
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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <seanjc@...gle.com>,
        Sandipan Das <sandipan.das@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Michael Roth <michael.roth@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Jan Kara <jack@...e.cz>, Ingo Molnar <mingo@...hat.com>,
        Huang Rui <ray.huang@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Brijesh Singh <brijesh.singh@....com>,
        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>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH kernel v2 2/3] KVM: SEV: Enable data breakpoints in SEV-ES

On 1/12/23 05:28, Borislav Petkov wrote:
> On Thu, Jan 12, 2023 at 04:45:34PM +1100, Alexey Kardashevskiy wrote:
>> Well, SEV-ES KVM (ES == Encrypted State) does not save/restore them for the
>> guest (well, as I would expect) as the guest registers are not visible to
>> host to save, they are intercepted and the VM does this GHCB dance with
>> VMGEXIT(SVM_EXIT_WRITE_DR7).
> 
> But they're saved in the VMSA, as Table B-3 says.

Correct, when this feature is enabled, the VMRUN execution will restore 
the guest debug registers on guest entry and save them on guest exit.

Thanks,
Tom

> 
>> Well, the only place in APM is that "Table B-3. Swap Types and the AMD APM
>> volume 2", and it is pretty brief, do I miss something?
> 
> I don't understand that question - please elaborate.
> 
> Thx.
>