linux-kernel - Re: [PATCH 3/4] x86/mce: Get rid of msr

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Date:   Wed, 22 Sep 2021 17:57:52 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Yazen Ghannam <yazen.ghannam@....com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86/mce: Get rid of msr_ops

On Wed, Sep 22, 2021 at 03:22:01PM +0000, Luck, Tony wrote:
> Also:
> 
> 	switch (enum) {
> 	actions for every value of that enum
> 	}
> 
> doesn't need a default: option

Right, my thought was to catch silly stuff like this here:

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index b355ce737543..dfecf65e5407 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1714,6 +1714,7 @@ static void __mcheck_cpu_init_clear_banks(void)
 			continue;
 		wrmsrl(mca_msr_reg(i, MCA_CTL), b->ctl);
 		wrmsrl(mca_msr_reg(i, MCA_STATUS), 0);
+		wrmsrl(mca_msr_reg(i, 12), 0);
 	}
 }
 

but we already warn nicely there:

[    0.146457] unchecked MSR access error: WRMSR to 0x0 (tried to write 0x0000000000000000) at rIP: 0xffffffff8103234b (__mcheck_cpu_init_clear_banks+0x6b/0xe0)
[    0.147550] Call Trace:
[    0.147836]  mcheck_cpu_init+0x16c/0x4a0
[    0.148234]  identify_cpu+0x3fe/0x670
[    0.148607]  identify_boot_cpu+0xc/0x94
[    0.148995]  check_bugs+0x26/0xaef
[    0.149353]  ? __get_locked_pte+0x14a/0x200
[    0.149777]  start_kernel+0x602/0x621
[    0.150153]  secondary_startup_64_no_verify+0xb0/0xbb

and the mce_rd/wrmsrl() wrappers even panic.

So default case gone.

-- 
Regards/Gruss,
    Boris.

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