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From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: David Laight <david.laight.linux@gmail.com>
Cc: <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
	<tglx@kernel.org>, <mingo@redhat.com>, <bp@alien8.de>,
	<dave.hansen@linux.intel.com>, <hpa@zytor.com>,
	Omar Avelar <omar.avelar@intel.com>, <stable@vger.kernel.org>,
	Miguel Ojeda <ojeda@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>
Subject: Re: [PATCH] x86/build/64: Prevent native builds from generating APX instructions
Date: Sun, 2 Aug 2026 14:32:32 -0700	[thread overview]
Message-ID: <762ba2f6-bfe1-461d-a46d-84f5f368445b@intel.com> (raw)
In-Reply-To: <20260802100808.754400af@pumpkin>

On 8/2/2026 2:08 AM, David Laight wrote:
> 
> Does that mean that this patch is completely unnecessary?
It is necessary. On APX systems running, e.g. Linux kernel v6.16+, with 
the OS enables XCR0.APX, the compiler may consider all 32 registers 
usable and the compiled kernel inadvertently emits APX instructions 
(unconditionally) clobbering those registers. So -mno apxf prevents such 
unintended in-kernel use.

Note that mainline currently supports only userspace APX, where user 
EGPR state is context-switched through the XSAVE mechanism. That alone 
is insufficient to support in-kernel uses. Like the legacy GPRs, EGPRs 
need to be handled on entry paths, and there are still many other things 
to consider before in-kernel usages.

Thanks,
Chang

      reply	other threads:[~2026-08-02 21:32 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-07-08 21:14 [PATCH] x86/build/64: Prevent native builds from generating APX instructions Chang S. Bae
2026-07-09 12:36 ` Miguel Ojeda
2026-07-14 22:15   ` Chang S. Bae
2026-07-15 10:30     ` Miguel Ojeda
2026-07-31 20:46       ` Chang S. Bae
2026-07-31 20:57         ` Miguel Ojeda
2026-07-31 21:15           ` Chang S. Bae
2026-07-12 20:25 ` Nathan Chancellor
2026-08-01 11:44 ` David Laight
2026-08-02  0:00   ` Chang S. Bae
2026-08-02  9:08     ` David Laight
2026-08-02 21:32       ` Chang S. Bae [this message]

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