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Re: [RFC PATCH 09/11] x86: Migrate spec_ctrl vendor checks to x86_vendor_is()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- From: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
- Date: Thu, 11 Dec 2025 17:58:34 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>, "Stefano Stabellini" <sstabellini@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 11 Dec 2025 16:59:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu Dec 11, 2025 at 4:38 PM CET, Andrew Cooper wrote:
> On 11/12/2025 10:31 am, Alejandro Vallejo wrote:
>> Seeing how both you and Andrew seem onboard with dropping cross-vendor
>> support
>
> I found another cross-vendor dropping which you'll want to look into.
>
> struct svm_vcpu contains three guest_sysenter_* MSRs.
>
> In AMD CPUs, these MSRs only have 32 bits of storage, with the upper
> halfs write-discard. They are switched via VMLOAD/VMSAVE.
>
> However, in the cross-vendor case, the upper halves are needed for 64bit
> kernels setting up SYSENTER support. Therefore, they're unconditionally
> intercepted so we can avoid losing the upper half.
>
> By dropping cross-vendor support, we can get rid of these fields, allow
> the guest unconditional access, and simply the MSR intercept logic a little.
>
> ~Andrew
Sounds straightforward, I'll add it to the pile.
Cheers,
Alejandro
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