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Re: [PATCH 2/3] x86/spec-ctrl: Drop SPEC_CTRL_{ENTRY_FROM,EXIT_TO}_HVM
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Fri, 14 Jan 2022 12:42:16 +0100
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Jan 13, 2022 at 04:38:32PM +0000, Andrew Cooper wrote:
> These were written before Spectre/Meltdown went public, and there was large
> uncertainty in how the protections would evolve. As it turns out, they're
> very specific to Intel hardware, and not very suitable for AMD.
>
> Expand and drop the macros. No change at all for VT-x.
>
> For AMD, the only relevant piece of functionality is DO_OVERWRITE_RSB,
> although we will soon be adding (different) logic to handle MSR_SPEC_CTRL.
>
> This has a marginal improvement of removing an unconditional pile of long-nops
> from the vmentry/exit path.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
I wonder however if it would be clearer to define
SPEC_CTRL_ENTRY_FROM_{SVM,VMX} and EXIT macros in spec_ctrl_asm.h
(even if just used in a single place) so that all the related SPEC
macros are in a single file.
Thanks, Roger.
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