linux-kernel - Re: [PATCH v5 05/16] x86/pvh: Use fixed_percpu

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Message-ID: <CAFULd4ZAFuGMdkXz_Lu0vrQHQG4CSgaJzuGSdM0abPpNOO8cPg@mail.gmail.com>
Date: Thu, 7 Nov 2024 15:30:26 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	Ingo Molnar <mingo@...nel.org>, "H . Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Borislav Petkov <bp@...en8.de>, Ard Biesheuvel <ardb@...nel.org>, Juergen Gross <jgross@...e.com>, 
	Boris Ostrovsky <boris.ostrovsky@...cle.com>, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v5 05/16] x86/pvh: Use fixed_percpu_data for early boot GSBASE

On Tue, Nov 5, 2024 at 4:58 PM Brian Gerst <brgerst@...il.com> wrote:
>
> Instead of having a private area for the stack canary, use
> fixed_percpu_data for GSBASE like the native kernel.
>
> Signed-off-by: Brian Gerst <brgerst@...il.com>
> ---

This patch looks like it could be submitted independently of the main
series and should include XEN maintainers (CC'd).

Uros.

>  arch/x86/platform/pvh/head.S | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
> index 64fca49cd88f..b0a9a58952aa 100644
> --- a/arch/x86/platform/pvh/head.S
> +++ b/arch/x86/platform/pvh/head.S
> @@ -159,10 +159,15 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
>  1:
>         UNWIND_HINT_END_OF_STACK
>
> -       /* Set base address in stack canary descriptor. */
> -       mov $MSR_GS_BASE,%ecx
> -       leal canary(%rip), %eax
> -       xor %edx, %edx
> +       /*
> +        * Set up GSBASE.
> +        * Note that, on SMP, the boot cpu uses init data section until
> +        * the per cpu areas are set up.
> +        */
> +       movl $MSR_GS_BASE,%ecx
> +       leaq INIT_PER_CPU_VAR(fixed_percpu_data)(%rip), %rdx
> +       movq %edx, %eax
> +       shrq $32, %rdx
>         wrmsr
>
>         /*
> @@ -232,8 +237,6 @@ SYM_DATA_START_LOCAL(gdt_start)
>  SYM_DATA_END_LABEL(gdt_start, SYM_L_LOCAL, gdt_end)
>
>         .balign 16
> -SYM_DATA_LOCAL(canary, .fill 48, 1, 0)
> -
>  SYM_DATA_START_LOCAL(early_stack)
>         .fill BOOT_STACK_SIZE, 1, 0
>  SYM_DATA_END_LABEL(early_stack, SYM_L_LOCAL, early_stack_end)
> --
> 2.47.0
>