linux-kernel - Re: [PATCH v2 1/2] x86/cpu: allow reducing x86_phys_bits during early_identify

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Message-ID: <hhzgb6ymqhba3snzk5zjorxr57h6jykaedqftgm2veapsazfnd@ldwehefzpkfx>
Date: Thu, 1 Feb 2024 10:33:55 +0200
From: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	Zixi Chen <zixchen@...hat.com>, Adam Dunlap <acdunlap@...gle.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Kai Huang <kai.huang@...el.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...nel.org>, x86@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] x86/cpu: allow reducing x86_phys_bits during
 early_identify_cpu()

On Thu, Feb 01, 2024 at 12:09:01AM +0100, Paolo Bonzini wrote:
> In commit fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct
> value straight away, instead of a two-phase approach"), the initialization
> of c->x86_phys_bits was moved after this_cpu->c_early_init(c).  This is
> incorrect because early_init_amd() expected to be able to reduce the
> value according to the contents of CPUID leaf 0x8000001f.
> 
> Fortunately, the bug was negated by init_amd()'s call to early_init_amd(),
> which does reduce x86_phys_bits in the end.  However, this is very
> late in the boot process and, most notably, the wrong value is used for
> x86_phys_bits when setting up MTRRs.
> 
> To fix this, call get_cpu_address_sizes() as soon as X86_FEATURE_CPUID is
> set/cleared, and c->extended_cpuid_level is retrieved.
> 
> Fixes: fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct value straight away, instead of a two-phase approach")
> Cc: Adam Dunlap <acdunlap@...gle.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Xiaoyao Li <xiaoyao.li@...el.com>
> Cc: Kai Huang <kai.huang@...el.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: x86@...nel.org
> Cc: stable@...r.kernel.org
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov