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Re: [PATCH] x86/SVM: restrict hardware SSBD update upon guest VIRT_SPEC_CTRL write
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 9 Dec 2022 11:11:29 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Fri, 09 Dec 2022 10:11:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09.12.2022 10:59, Roger Pau Monné wrote:
> On Thu, Dec 08, 2022 at 12:24:54PM +0100, Jan Beulich wrote:
>> --- a/xen/arch/x86/msr.c
>> +++ b/xen/arch/x86/msr.c
>> @@ -699,12 +699,16 @@ int guest_wrmsr(struct vcpu *v, uint32_t
>> }
>> else
>
> I think you could turn this into an `else if` and check if the new
> value and the current one differ on the SSBD bit?
I'd prefer not to: Keeping it as I have it will likely reduce code churn
if a 2nd bit wants supporting in that MSR.
> Provided it fixes the issue:
>
> Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Thanks, but I'm a little puzzled by the constraint: Imo even if this
doesn't address the observed issue, it still fixes one aspect of wrong
behavior here. The sole difference then would be that the Reported-by:
would go away.
Jan
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