linux-kernel - Re: [RFC][PATCH 04/34] x86/mm: Introduce physical address limit helper

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Date: Tue, 27 Feb 2024 11:05:29 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "rafael@...nel.org" <rafael@...nel.org>,
	"lenb@...nel.org" <lenb@...nel.org>, "x86@...nel.org" <x86@...nel.org>,
	"bp@...en8.de" <bp@...en8.de>
Subject: Re: [RFC][PATCH 04/34] x86/mm: Introduce physical address limit
 helper

On Thu, 2024-02-22 at 10:39 -0800, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Modern processors enumerate the sizes of the physical and virtual address
> spaces that they can handle.  The kernel stashes this information for each
> CPU in 'cpuinfo_x86'.
> 
> Like a lot of system-wide configuration, in practice the kernel only uses
> this information from the boot CPU.  That makes a lot of sense because
> the kernel can't practically support two CPUs with such different
> fundamental support as the size of the address spaces.
> 
> Having a per-cpu copy of this data is silly.  It is, at best, a waste
> of space to keep it around for the non-boot CPUs.  At worst, it is yet
> another bit of data that must be initialized in a particular order and
> can be a source of bugs.
> 
> Introduce a helper to look up the number of supported physical address bits:
> 
> 	x86_phys_bits()
> 
> Replace most open-coded references to boot_cpu_data.x86_phys_bits.
> 
> This form is more compact and also opens up the door to adding some
> centralized checking and enforcing rules around this important system-
> wide value.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Len Brown <lenb@...nel.org>
> ---
> 

Reviewed-by: Kai Huang <kai.huang@...el.com>