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Re: [PATCH 1/3] x86/kexec: Drop compatibility_mode_far
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Feb 2023 11:34:26 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Feb 2023 10:34:31 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.02.2023 18:48, Andrew Cooper wrote:
> ljmp is (famously?) incompatible between Intel and AMD CPUs, and while we're
> using one of the compatible forms, we've got a good stack and lret is the far
> more common way of doing this.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
One question though:
> --- a/xen/arch/x86/x86_64/kexec_reloc.S
> +++ b/xen/arch/x86/x86_64/kexec_reloc.S
> @@ -86,12 +86,11 @@ ENTRY(kexec_reloc)
> movq %rax, (compat_mode_gdt_desc + 2)(%rip)
> lgdt compat_mode_gdt_desc(%rip)
>
> - /* Relocate compatibility mode entry point address. */
> - leal compatibility_mode(%rip), %eax
> - movl %eax, compatibility_mode_far(%rip)
> -
> /* Enter compatibility mode. */
> - ljmp *compatibility_mode_far(%rip)
> + lea compatibility_mode(%rip), %rax
> + push $0x10
Any thought about making this literal number a proper expression,
rendering the code a little less fragile?
Jan
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