linux-kernel - Re: [PATCH 3/5] x86/pvh: Set phys_base when calling xen_prepare

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Message-ID: <9cddfb9d-0627-4f00-b027-4cb1bbdfad4f@suse.com>
Date: Thu, 23 May 2024 13:14:40 +0200
From: Jürgen Groß <jgross@...e.com>
To: Jason Andryuk <jason.andryuk@....com>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 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>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] x86/pvh: Set phys_base when calling xen_prepare_pvh()

On 10.04.24 21:48, Jason Andryuk wrote:
> phys_base needs to be set for __pa() to work in xen_pvh_init() when
> finding the hypercall page.  Set it before calling into
> xen_prepare_pvh(), which calls xen_pvh_init().  Clear it afterward to
> avoid __startup_64() adding to it and creating an incorrect value.
> 
> Signed-off-by: Jason Andryuk <jason.andryuk@....com>
> ---
> Instead of setting and clearing phys_base, a dedicated variable could be
> used just for the hypercall page.  Having phys_base set properly may
> avoid further issues if the use of phys_base or __pa() grows.
> ---
>   arch/x86/platform/pvh/head.S | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
> index bb1e582e32b1..c08d08d8cc92 100644
> --- a/arch/x86/platform/pvh/head.S
> +++ b/arch/x86/platform/pvh/head.S
> @@ -125,7 +125,17 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
>   	xor %edx, %edx
>   	wrmsr
>   
> +	/* Calculate load offset from LOAD_PHYSICAL_ADDR and store in
> +	 * phys_base.  __pa() needs phys_base set to calculate the
> +	 * hypercall page in xen_pvh_init(). */

Please use the correct style for multi-line comments:

	/*
	 * comment lines
	 * comment lines
	 */

> +	movq %rbp, %rbx
> +	subq $LOAD_PHYSICAL_ADDR, %rbx
> +	movq %rbx, phys_base(%rip)
>   	call xen_prepare_pvh
> +	/* Clear phys_base.  __startup_64 will *add* to its value,
> +	 * so reset to 0. */

Comment style again.

> +	xor  %rbx, %rbx
> +	movq %rbx, phys_base(%rip)
>   
>   	/* startup_64 expects boot_params in %rsi. */
>   	lea rva(pvh_bootparams)(%ebp), %rsi

With above fixed:

Reviewed-by: Juergen Gross <jgross@...e.com>

Juergen