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Re: [Xen-devel] [PATCH] SVM: limit GIF=0 region
- To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Mon, 10 Sep 2018 18:12:21 -0400
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Brian Woods <brian.woods@xxxxxxx>, Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
- Delivery-date: Mon, 10 Sep 2018 22:11:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 09/10/2018 11:02 AM, Jan Beulich wrote:
> Use EFLAGS.IF for most ordinary purposes; there's in particular no need
> to unduly defer NMI/#MC. Clear GIF only immediately before VMRUN itself.
> This has the additional advantage that svm_stgi_label now indeed marks
> the only place where GIF gets set.
>
> Note regarding the main STI placement: Quite counterintuitively the
> host's EFLAGS.IF continues to have a meaning while the guest runs; see
> PM Vol 2 section "Physical (INTR) Interrupt Masking in EFLAGS". Hence we
> need to set the flag for the duration of time being in guest context.
> However, SPEC_CTRL_ENTRY_FROM_HVM wants to be carried out with EFLAGS.IF
> clear.
>
> Note regarding the main STGI placement: It could be moved further up,
> but at present SPEC_CTRL_EXIT_TO_HVM is not NMI/#MC-safe.
>
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
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