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Re: [PATCH for-4.19 v4.5 2/7] x86/xstate: Cross-check dynamic XSTATE sizes at boot
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 19 Jun 2024 13:51:41 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 19 Jun 2024 11:51:54 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 19.06.2024 12:46, Andrew Cooper wrote:
> Right now, xstate_ctxt_size() performs a cross-check of size with CPUID in for
> every call. This is expensive, being used for domain create/migrate, as well
> as to service certain guest CPUID instructions.
>
> Instead, arrange to check the sizes once at boot. See the code comments for
> details. Right now, it just checks hardware against the algorithm
> expectations. Later patches will cross-check Xen's XSTATE calculations too.
>
> Introduce more X86_XCR0_* and X86_XSS_* constants CPUID bits. This is to
> maximise coverage in the sanity check, even if we don't expect to
> use/virtualise some of these features any time soon. Leave HDC and HWP alone
> for now; we don't have CPUID bits from them stored nicely.
>
> Only perform the cross-checks when SELF_TESTS are active. It's only
> developers or new hardware liable to trip these checks, and Xen at least
> tracks "maximum value ever seen in xcr0" for the lifetime of the VM, which we
> don't want to be tickling in the general case.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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