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Re: [PATCH v2] x86/svm: Separate STI and VMRUN instructions in svm_asm_do_resume()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 18 Feb 2025 15:42:21 +0100
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- Delivery-date: Tue, 18 Feb 2025 14:42:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18.02.2025 15:37, Andrew Cooper wrote:
> There is a corner case in the VMRUN instruction where its INTR_SHADOW state
> leaks into guest state if a VMExit occurs before the VMRUN is complete. An
> example of this could be taking #NPF due to event injection.
>
> Xen can safely execute STI anywhere between CLGI and VMRUN, as CLGI blocks
> external interrupts too. However, an exception (while fatal) will appear to
> be in an irqs-on region (as GIF isn't considered), so position the STI after
> the speculation actions but prior to the GPR pops.
>
> Link:
> https://lore.kernel.org/all/CADH9ctBs1YPmE4aCfGPNBwA10cA8RuAk2gO7542DjMZgs4uzJQ@xxxxxxxxxxxxxx/
> Fixes: 66b245d9eaeb ("SVM: limit GIF=0 region")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2:
> * Move after the speculation actions.
>
> Emailed out just for completeness. I've queued it in my for-4.21 branch.
It'll want backporting, so I wonder if we should persuade Oleksii into
taking it for 4.20.
Jan
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