linux-kernel - Re: [PATCH] x86/vmware: Fix hypercall clobbers

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Message-ID: <kv4bv3jng2iap3qwvk36pciggiho4yhavnfvsisri67jkdt6kr@szokbl6qdibl>
Date: Fri, 30 Jan 2026 08:46:48 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Thorsten Leemhuis <regressions@...mhuis.info>
Cc: Alexey Makhalov <alexey.makhalov@...adcom.com>, x86@...nel.org, 
	linux-kernel@...r.kernel.org, Ajay Kaher <ajay.kaher@...adcom.com>, 
	bcm-kernel-feedback-list@...adcom.com, Peter Zijlstra <peterz@...radead.org>, 
	Justin Forbes <jforbes@...oraproject.org>, Linux kernel regressions list <regressions@...ts.linux.dev>, 
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86/vmware: Fix hypercall clobbers

On Fri, Jan 30, 2026 at 05:24:02PM +0100, Thorsten Leemhuis wrote:
> [CCing Linus, maybe we still can get this fixed for -rc8 or at least final]
> 
> On 1/23/26 18:35, Josh Poimboeuf wrote:
> > On Fri, Jan 23, 2026 at 10:47:18AM +0100, Thorsten Leemhuis wrote:
> >> [CCing the regression list]
> >>
> >> On 1/22/26 11:00, Alexey Makhalov wrote:
> >>>
> >>> Thanks for reporting the problem.
> >>> [...] 
> >>> Workarounding QEMU misbehavior from the kernel side by introducing less
> >>> efficient asm inlines does not sound correct.
> >>
> >> Well, fixing bugs right where they are obviously is a good thing.
> >>
> >> But well, the problem according to the description quoted below was
> >> exposed by a change that went into 6.19-rc1 -- which makes it a kernel
> >> regression that must be fixed in the kernel (ideally before 6.19 is out).
> >>
> >> At least from my understanding of Linus point of view on situations like
> >> that. Or am I mistaken for some reason?
> >>
> >> Or is this a case of "we for now assume this is such a corner case that
> >> nobody else will hit; if we are wrong we'll reconsider".
> > 
> > Hm, yes, from that perspective I agree this is a kernel regression that
> > needs fixed.  We still want Linux to work with older "broken" versions
> > of qemu that clobber registers.
> 
> Josh, what's the status here? From here it looks like nothing happened
> during the last week. Should we move on with the patch at the start of
> this thread? Or is "widening the hypercall just for
> VMWARE_CMD_ABSPOINTER_DATA" as suggested by Alexey elsewhere in this
> thread a better fix? Or would temporarily reverting aca282ab7e75
> ("x86/asm: Annotate special section entries") be the best move for now?

I think we still need to go with the original patch at the start of this
thread.  There's nothing preventing the compiler from doing similar
optimizations for the other hypercalls.

-- 
Josh