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Re: [PATCH v1] x86/nestedsvm: honour L2's EFLAGS.IF when L1 clears V_INTR_MASKING
- To: ross.lagerwall@xxxxxxxxxx
- From: chunjie.zhu@xxxxxxxxxx
- Date: Tue, 3 Nov 2026 18:11:34 +0800
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- Cc: andrew.cooper3@xxxxxxxxxx, chunjie.zhu@xxxxxxxxxx, jason.andryuk@xxxxxxx, jbeulich@xxxxxxxx, roger@xxxxxxxxxxxxxx, teddy.astie@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 03 Nov 2026 10:12:00 +0000
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On Thu, Oct 29, 2026 at 17:20, Ross Lagerwall wrote:
> Would it not make sense to check this in nsvm_intr_blocked() instead?
> There is already a similar (inverse) check there so extending that seems
> more logical to me.
Thanks for the suggestion, but I think there would be a regression.
nsvm_intr_blocked() has no access to the intack. Per the APM (vol.2,
section 15.21), V_INTR_MASKING controls whether the masking of interrupts
(EFLAGS.IF and TPR) is to be virtualized. That masking only applies to
maskable external interrupts (PIC/LAPIC/vector). NMI is not masked by
IF/TPR, and #MC is an exception, so neither is affected.
With the check moved into nsvm_intr_blocked(), an NMI/#MC aimed at L1
would be held pending whenever V_INTR_MASKING=0 and L2's IF is clear,
which would be a regression for L1 hypervisors that intercept NMI/#MC.
So I would prefer to keep the check in the hvm_intsrc_pic/lapic/vector
case of nestedsvm_vcpu_interrupt(), where the source is known. If you
would rather have it in nsvm_intr_blocked(), I can instead pass the
intack down (changing nhvm_interrupt_blocked()) so that the IF check
is applied to non-NMI/MCE sources only.
Let me know which you prefer.
Regards,
Chunjie
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