linux-kernel - Re: [Question PATCH kernel] x86/amd/sev/nmi+vc: Fix stack handling (why is this happening?)

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Message-ID: <Y9jX9AKYP8H34wGI@8bytes.org>
Date:   Tue, 31 Jan 2023 09:57:24 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Alexey Kardashevskiy <aik@....com>,
        Peter Zijlstra <peterz@...radead.org>, kvm@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <seanjc@...gle.com>,
        Jiri Kosina <jkosina@...e.cz>, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [Question PATCH kernel] x86/amd/sev/nmi+vc: Fix stack handling
 (why is this happening?)

On Mon, Jan 30, 2023 at 09:30:38AM -0800, H. Peter Anvin wrote:
> It's somewhat odd to me that reading %dr7 is volatile, but %dr6 is
> not... %dr6 is the status register!

The reason is that on SEV-ES only accesses to DR7 will cause #VC
exceptions, DR0-DR6 are not intercepted.

Regards,

	Joerg