linux-kernel - Re: [PATCHv9 04/16] x86/cpu: Defer CR pinning setup until core initcall

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Message-ID: <aa4sycdhtxlerad6a7xucf6icjyioydu7oefvsdvwnoozqd2kh@lhtkexpqjebn>
Date: Wed, 9 Jul 2025 12:38:39 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Sohil Mehta <sohil.mehta@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ard Biesheuvel <ardb@...nel.org>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Xiongwei Song <xiongwei.song@...driver.com>, Xin Li <xin3.li@...el.com>, 
	"Mike Rapoport (IBM)" <rppt@...nel.org>, Brijesh Singh <brijesh.singh@....com>, 
	Michael Roth <michael.roth@....com>, Tony Luck <tony.luck@...el.com>, 
	Alexey Kardashevskiy <aik@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...nel.org>, 
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Daniel Sneddon <daniel.sneddon@...ux.intel.com>, 
	Kai Huang <kai.huang@...el.com>, Sandipan Das <sandipan.das@....com>, 
	Breno Leitao <leitao@...ian.org>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
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	Andrew Morton <akpm@...ux-foundation.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Yuntao Wang <ytcoode@...il.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, Tejun Heo <tj@...nel.org>, Changbin Du <changbin.du@...wei.com>, 
	Huang Shijie <shijie@...amperecomputing.com>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Namhyung Kim <namhyung@...nel.org>, Arnaldo Carvalho de Melo <acme@...hat.com>, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCHv9 04/16] x86/cpu: Defer CR pinning setup until core
 initcall

On Tue, Jul 08, 2025 at 06:19:03PM -0700, Sohil Mehta wrote:
> On 7/7/2025 1:03 AM, Kirill A. Shutemov wrote:
> > From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > 
> > In order to map the EFI runtime services, set_virtual_address_map()
> > needs to be called, which resides in the lower half of the address
> > space. This means that LASS needs to be temporarily disabled around
> > this call. This can only be done before the CR pinning is set up.
> > 
> > Instead of moving setup_cr_pinning() below efi_enter_virtual_mode() in
> > arch_cpu_finalize_init(), defer it until core initcall.
> > 
> > Wrapping efi_enter_virtual_mode() into lass_stac()/clac() is not enough
> > because AC flag gates data accesses, but not instruction fetch. Clearing
> > the CR4 bit is required.
> > 
> 
> I think the wording might need to be reordered. How about?
> 
> In order to map the EFI runtime services, set_virtual_address_map()
> needs to be called, which resides in the lower half of the address
> space. This means that LASS needs to be temporarily disabled around
> this call.
> 
> Wrapping efi_enter_virtual_mode() into lass_stac()/clac() is not enough
> because AC flag gates data accesses, but not instruction fetch. Clearing
> the CR4 bit is required.
> 
> However, this must be done before the CR pinning is set up. Instead of
> arbitrarily moving setup_cr_pinning() after efi_enter_virtual_mode() in
> arch_cpu_finalize_init(), defer it until core initcall.
> 
> Other than that,
> Reviewed-by: Sohil Mehta <sohil.mehta@...el.com>

Okay, looks good, thanks!

-- 
  Kiryl Shutsemau / Kirill A. Shutemov