linux-kernel - Re: [tip: x86/urgent] x86/cpu: Provide default cache line size if not enumerated

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Message-ID: <f12ab64f-fd59-491e-a44a-6ae570a81ada@heusipp.de>
Date: Thu, 30 May 2024 17:05:33 +0200
From: Jörn Heusipp <osmanx@...sipp.de>
To: linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 stable@...r.kernel.org, x86@...nel.org, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Adam Dunlap <acdunlap@...gle.com>
Subject: Re: [tip: x86/urgent] x86/cpu: Provide default cache line size if not
 enumerated


Hello Dave!

On 30/05/2024 16:23, tip-bot2 for Dave Hansen wrote:
> The following commit has been merged into the x86/urgent branch of tip:
>
> Commit-ID:     b9210e56d71d9deb1ad692e405f6b2394f7baa4d
> Gitweb:        https://git.kernel.org/tip/b9210e56d71d9deb1ad692e405f6b2394f7baa4d
> Author:        Dave Hansen <dave.hansen@...ux.intel.com>
> AuthorDate:    Fri, 17 May 2024 13:05:34 -07:00
> Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
> CommitterDate: Thu, 30 May 2024 07:14:27 -07:00

> Tested-by: Jörn Heusipp <osmanx@...sipp.de>

> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 2b170da..373b16b 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1070,6 +1070,10 @@ void get_cpu_address_sizes(struct cpuinfo_x86 *c)
>   			    cpu_has(c, X86_FEATURE_PSE36))
>   				c->x86_phys_bits = 36;
>   		}
> +
> +		/* Provide a sane default if not enumerated: */
> +		if (!c->x86_clflush_size)
> +			c->x86_clflush_size = 32;
>   	} else {
>   		cpuid(0x80000008, &eax, &ebx, &ecx, &edx);
>

That honestly looks like a mis-merge to me. This is not what I did test.
x86_clflush_size needs to get set in the top-level else branch in which
it is not already set. commit 95bfb35269b2e85cff0dd2c957b2d42ebf95ae5f
had switched the if branches around.

Best regards,
Jörn