From: Dave Hansen <dave.hansen@intel.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
LKML <linux-kernel@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR
Date: Wed, 2 Apr 2025 10:35:03 -0700 [thread overview]
Message-ID: <67274a07-eac9-4d60-9737-c730c25a9fea@intel.com> (raw)
In-Reply-To: <20250402172458.1378112-1-andrew.cooper3@citrix.com>
On 4/2/25 10:24, Andrew Cooper wrote:
...
> i.e. The SDM was incorrect at the time, and barriers should not have been
> inserted. Double checking the original AAI65 errata (not available from
> intel.com any more) shows no mention of barriers either.
>
> Note: If this were a general codepath, the MFENCEs would be needed, because
> AMD CPUs of the same vintage do sport otherwise-unordered CLFLUSHs.
>
> Furthermore, use a plain alternative, rather than static_cpu_has_bug() and/or
> no optimisation. The workaround is a single instruction.
Nit: this never comes out and says that it removes the unnecessary
barriers. But we can fix that up when we apply this by adding:
Remove the unnecessary barriers. Furthermore, use a plain
alternative, rather than static_cpu_has_bug() and/or
no optimisation. The workaround is a single instruction.
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
next prev parent reply other threads:[~2025-04-02 17:39 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-02 17:24 [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR Andrew Cooper
2025-04-02 17:35 ` Dave Hansen [this message]
2025-04-02 20:04 ` Ingo Molnar
2025-04-02 19:35 ` [tip: x86/mm] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR in mwait_idle_with_hints() and prefer_mwait_c1_over_halt() tip-bot2 for Andrew Cooper
2025-04-02 20:32 ` tip-bot2 for Andrew Cooper
2025-04-04 14:14 ` [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR Uros Bizjak
2025-04-04 14:16 ` Andrew Cooper
2025-04-04 14:49 ` Uros Bizjak
2025-04-06 17:21 ` Ingo Molnar
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