From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Yi Lai <yi1.lai@intel.com>, Thomas Gleixner <tglx@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>, Xin Li <xin@zytor.com>,
x86@kernel.org, hpa@zytor.com, Shuah Khan <shuah@kernel.org>,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
yi1.lai@linux.intel.com
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v2] selftests/x86: Fix sysret_rip assertion failure on FRED systems
Date: Tue, 24 Mar 2026 10:11:20 +0000 [thread overview]
Message-ID: <dc56dd78-fd72-4d29-a355-8c4243dca2e0@citrix.com> (raw)
In-Reply-To: <20260324085102.688490-1-yi1.lai@intel.com>
On 24/03/2026 8:51 am, Yi Lai wrote:
> The existing 'sysret_rip' selftest asserts that 'regs->r11 ==
> regs->flags'. This check relies on the behavior of the SYSCALL
> instruction on legacy x86_64, which saves 'RFLAGS' into 'R11'.
>
> However, on systems with FRED (Flexible Return and Event Delivery)
> enabled, instead of using registers, all state is saved onto the stack.
> Consequently, 'R11' retains its userspace value, causing the assertion
> to fail.
>
> Fix this by detecting if FRED is enabled and skipping the register
> assertion in that case. The detection is done by checking if the RPL
> bits of the GS selector are preserved after a hardware exception.
> IDT (via IRET) clears the RPL bits of NULL selectors, while FRED (via
> ERETU) preserves them.
>
> Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Yi Lai <yi1.lai@intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
next prev parent reply other threads:[~2026-03-24 10:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-24 8:51 [PATCH v2] selftests/x86: Fix sysret_rip assertion failure on FRED systems Yi Lai
2026-03-24 10:11 ` Andrew Cooper [this message]
2026-03-24 16:14 ` Xin Li
2026-03-26 4:37 ` Lai, Yi
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