linux-kernel - Re: [PATCH] x86/hyperv: use helpers to read control registers in hv_snp_boot

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Message-ID: <CAJD7tkbkayNvptAR8fNwd-p7bLcxhV40TfkEUGQYYK1N=_VFww@mail.gmail.com>
Date: Thu, 1 Aug 2024 11:41:23 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: "K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, 
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>
Cc: 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>, linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/hyperv: use helpers to read control registers in hv_snp_boot_ap()

On Thu, Aug 1, 2024 at 11:40 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> Use native_read_cr*() helpers to read control registers into vmsa->cr*
> instead of open-coded assembly.
>
> No functional change intended, unless there was a purpose to specifying
> rax.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
>  arch/x86/hyperv/ivm.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index b4a851d27c7cb..434507dd135c5 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -321,9 +321,9 @@ int hv_snp_boot_ap(u32 cpu, unsigned long start_ip)
>
>         vmsa->efer = native_read_msr(MSR_EFER);
>
> -       asm volatile("movq %%cr4, %%rax;" : "=a" (vmsa->cr4));
> -       asm volatile("movq %%cr3, %%rax;" : "=a" (vmsa->cr3));
> -       asm volatile("movq %%cr0, %%rax;" : "=a" (vmsa->cr0));
> +       vmsa->cr4 = native_read_cr4();
> +       vmsa->cr3 = __native_read_cr3();
> +       vmsa->cr3 = native_read_cr0();

..and obviously this should be vmsa->cr0, forgot to regenerate the
patch after amending, apologies.

>
>         vmsa->xcr0 = 1;
>         vmsa->g_pat = HV_AP_INIT_GPAT_DEFAULT;
> --
> 2.46.0.rc2.264.g509ed76dc8-goog
>