linux-kernel - Re: [PATCH V2 1/1] x86/tdx: Route safe halt execution via tdx_safe

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Message-ID: <702c5acb-6bab-4940-a8f1-c346373167bd@intel.com>
Date: Mon, 3 Feb 2025 13:19:46 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Vishal Annapurve <vannapurve@...gle.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org, pbonzini@...hat.com, seanjc@...gle.com,
 erdemaktas@...gle.com, ackerleytng@...gle.com, jxgao@...gle.com,
 sagis@...gle.com, oupton@...gle.com, pgonda@...gle.com,
 dave.hansen@...ux.intel.com, linux-coco@...ts.linux.dev,
 chao.p.peng@...ux.intel.com, isaku.yamahata@...il.com, stable@...r.kernel.org
Subject: Re: [PATCH V2 1/1] x86/tdx: Route safe halt execution via
 tdx_safe_halt()

On 2/3/25 12:09, Kirill A. Shutemov wrote:
...
> But Sean's proposal with HLT check before enabling interrupts looks better
> to me.

"Sean's proposal" being this:

	https://lore.kernel.org/all/Z5l6L3Hen9_Y3SGC@google.com/

?

Is that just intended to quietly fix up a hlt-induced #VE? I'm not sure
that's a good idea. The TDVMCALL is slow, but the #VE is also presumably
quite slow. This is (presumably) getting called in an idle path which is
actually one of the most performance-sensitive things we have in the kernel.

Or am I missing the point of Sean's proposal?

I don't mind having the #VE handler warn about the situation if we end
up there accidentally.

I'd much rather have a kernel configured in a way that we are pretty
sure there's no path to even call hlt.