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Re: [PATCH] x86/hvm: Improve hvm_set_guest_pat() code generation
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 13 Jan 2022 15:38:04 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 13 Jan 2022 14:38:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.01.2022 14:50, Andrew Cooper wrote:
> This is a fastpath on virtual vmentry/exit, and forcing guest_pat to be
> spilled to the stack is bad. Performing the shift in a register is far more
> efficient.
>
> Drop the (IMO useless) log message. MSR_PAT only gets altered on boot, and a
> bad value will be entirely evident in the ensuing #GP backtrace.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
I'm curious though why ...
> @@ -313,10 +313,9 @@ int hvm_set_guest_pat(struct vcpu *v, u64 guest_pat)
> case PAT_TYPE_WRCOMB:
> case PAT_TYPE_WRPROT:
> case PAT_TYPE_WRTHROUGH:
> - break;
> + continue;
... you're going from "break" to "continue" here.
Jan
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