From: Borislav Petkov <bp@alien8.de>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alexey Kardashevskiy <aik@amd.com>,
Joerg Roedel <joro@8bytes.org>,
Peter Zijlstra <peterz@infradead.org>,
kvm@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Sean Christopherson <seanjc@google.com>,
Jiri Kosina <jkosina@suse.cz>, Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [Question PATCH kernel] x86/amd/sev/nmi+vc: Fix stack handling (why is this happening?)
Date: Mon, 30 Jan 2023 19:04:50 +0100 [thread overview]
Message-ID: <Y9gGwtS2tm5BKvmv@zn.tnic> (raw)
In-Reply-To: <38C572D7-E637-48C2-A57A-E62D44FF19BB@zytor.com>
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!
Yeah, as a precaution I think we should make all those volatile. Just in
case.
> I believe they should all be volatile (the compiler semantics is that
> volatile operations are always executed exactly once, in strict
> program order with respect to any other volatile operations); the real
> question is if there should also be memory clobbers on %dr6 reads and
> any %dr write.
Yes, I think so too. From gcc docs:
"6.47.2.1 Volatile
.................
...
Note that the compiler can move even 'volatile asm' instructions
relative to other code, including across jump instructions."
We already have __FORCE_ORDER for exactly things like that.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2023-01-30 18:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-27 3:56 [Question PATCH kernel] x86/amd/sev/nmi+vc: Fix stack handling (why is this happening?) Alexey Kardashevskiy
2023-01-27 9:08 ` Peter Zijlstra
2023-01-27 10:37 ` Joerg Roedel
2023-01-27 11:56 ` Alexey Kardashevskiy
2023-01-27 12:59 ` Joerg Roedel
2023-01-27 17:25 ` Joerg Roedel
2023-01-28 11:24 ` Alexey Kardashevskiy
2023-01-28 13:52 ` Joerg Roedel
2023-01-30 9:17 ` Joerg Roedel
2023-01-30 17:30 ` H. Peter Anvin
2023-01-30 18:04 ` Borislav Petkov [this message]
2023-01-31 8:57 ` Joerg Roedel
2023-01-31 15:53 ` Sean Christopherson
2023-01-31 16:00 ` Joerg Roedel
2023-01-31 16:47 ` Sean Christopherson
2023-01-27 12:13 ` Alexey Kardashevskiy
2023-01-27 12:41 ` Peter Zijlstra
2023-01-31 10:37 ` [tip: x86/urgent] x86/debug: Fix stack recursion caused by wrongly ordered DR7 accesses tip-bot2 for Joerg Roedel
2023-01-31 11:57 ` tip-bot2 for Joerg Roedel
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