linux-kernel - Re: [PATCH] x86/cpu/intel: Detect TME keyid bits before setting MTRR mask registers

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Date: Wed, 31 Jan 2024 10:39:14 +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>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Kai Huang <kai.huang@...ux.intel.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] x86/cpu/intel: Detect TME keyid bits before setting MTRR
 mask registers

On Tue, Jan 30, 2024 at 07:04:00PM +0100, Paolo Bonzini wrote:
> MKTME repurposes the high bit of physical address to key id for encryption
> key and, even though MAXPHYADDR in CPUID[0x80000008] remains the same,
> the valid bits in the MTRR mask register are based on the reduced number
> of physical address bits.
> 
> detect_tme() in arch/x86/kernel/cpu/intel.c detects TME and subtracts
> it from the total usable physical bits, but it is called too late.
> Move the call to early_init_intel() so that it is called in setup_arch(),
> before MTRRs are setup.
> 
> This fixes boot on some TDX-enabled systems which until now only worked
> with "disable_mtrr_cleanup".  Without the patch, the values written to
> the MTRRs mask registers were 52-bit wide (e.g. 0x000fffff_80000800)
> and the writes failed; with the patch, the values are 46-bit wide,
> which matches the reduced MAXPHYADDR that is shown in /proc/cpuinfo.
> 
> Fixes: cb06d8e3d020 ("x86/tme: Detect if TME and MKTME is activated by BIOS", 2018-03-12)
> Reported-by: Zixi Chen <zixchen@...hat.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Xiaoyao Li <xiaoyao.li@...el.com>
> Cc: Kai Huang <kai.huang@...ux.intel.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>

I've seen the patch before, although by different author and with
different commit message, not sure what is going on.

I had concern about that patch and I don't think it was addressed.
See the thread:

https://lore.kernel.org/all/20231002224752.33qa2lq7q2w4nqws@box

-- 
  Kiryl Shutsemau / Kirill A. Shutemov