linux-kernel - Re: [PATCH v1] x86/apic: Fix kernel panic when "intremap=off" and "x2apic

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Message-ID: <20230619145012.GCZJBrJKuiape5djVt@fat_crate.local>
Date:   Mon, 19 Jun 2023 16:50:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        gorcunov@...nvz.org, suresh.b.siddha@...el.com,
        Kishon Vijay Abraham I <kvijayab@....com>,
        Vasant Hegde <vasant.hegde@....com>
Subject: Re: [PATCH v1] x86/apic: Fix kernel panic when "intremap=off" and
 "x2apic_phys" are set

On Sat, Jun 17, 2023 at 02:52:36AM +0530, Dheeraj Kumar Srivastava wrote:
> x2APIC mode requires "Interrupt Remapping" to be enabled and the
> "physical x2apic" driver can be used only when x2APIC mode is enabled.
> However when "intremap=off" and "x2apic_phys" kernel command line
> parameters are passed, "physical x2apic" driver is being used even when
> x2APIC mode is disabled ("intremap=off" disables x2APIC mode).
> This results in the below kernel panic:
> 
>   unchecked MSR access error: RDMSR from 0x80f at rIP: 0xffffffff87eab4ec

Not a kernel panic - that's a warning about accessing a non-existent
MSR.

Can you send full dmesg? Privately is fine too.

How exactly do you trigger this? What hw?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette