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From:   Christian Lamparter <chunkeey@gmail.com>
To:     linux-kernel@vger.kernel.org
Cc:     x86@kernel.org, seanjc@google.com, klaus.espenlaub@oracle.com,
        bp@alien8.de, glx@linutronix.de, mingo@redhat.com,
        dave.hansen@linux.intel.com, hpa@zytor.com
Subject: Re: [PATCH  v1] x86/cpu/cacheinfo: fix panic on Ryzen Mobile 7x40 series in
 VBox VM
Date:   Tue, 17 Oct 2023 21:30:17 +0200
Message-ID: <4550917.LvFx2qVVIh@shift>
In-Reply-To: <652989ad8a7f110bad16cf1244c4c68a823f0afe.1693606609.git.chunkeey@gmail.com>
References: <652989ad8a7f110bad16cf1244c4c68a823f0afe.1693606609.git.chunkeey@gmail.com>
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Heads up!

Oracle addressed this with their virtualbox 7.0.12 release.
If you are affected, try it!

On Saturday, September 2, 2023 12:19:11 AM CEST Christian Lamparter wrote:
> Ryzen Mobile 7x40 chips experience an early kernel fault
> (division by zero) due to nonexistent input validation
> from CPUID data in amd_cpuid4().
> 
> This error was first reported on reddit [0] for a
> "AMD Ryzen 9 7940HS w/ Radeon 780M Graphics", but since then
> the bug has been reproduced on a "AMD Ryzen 7 7840HS" Laptop
> too.
> 
> [...]
> 
> The reason why this is happening is because the Ryzen CPU reports in its
> CPUID 80000006 edx register (which contains the L3 Cache Information)
> the value "00009000". This magic value means according to AMD's
> "AMD64 Architecture Programmer's Manual Volume 3" Table E-4.
> "L2/L3 Cache and TLB Associativity Field Encoding":
> 
> | Value for all fields should be determinded from Fn8000_001D.
> 
> (This means to look in cpuid(0x8000001D,...) instead.)
> 
> So, amd_cpuid4() is missing this special case. A case which has been
> present - according to this AMD Community post [1] - since
> Zen 2/Ryzen 3000 Series.
> 
> But wait, why is this only happening with Linux' when running under
> VirtualBox with these Ryzen Mobile CPUs and not when running natively?
> [...]