Re: [PATCH 2/2] x86/kvm/vmx: Fix VMX vs hrtimer_rearm_deferred()

[David Woodhouse <dwmw2@infradead.org>]

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On Thu, 2026-04-23 at 17:56 +0200, Peter Zijlstra wrote:
> Vishal reported that KVM unit test 'x2apic' started failing after commit
> 0e98eb14814e ("entry: Prepare for deferred hrtimer rearming").
> 
> The reason is that KVM/VMX is injecting interrupts while it has IRQs disabled,
> for a context that will enable IRQs, this means that regs->flags.X86_EFLAGS_IF
> == 0 and the irqentry_exit() will not DTRT.
> 
> Notably, irqentry_exit() must not call hrtimer_rearm_deferred() when the return
> context does not have IF set, because this will cause problems vs NMIs.
> 
> Therefore, fix up the state after the injection.
> 
> Fixes: 0e98eb14814e ("entry: Prepare for deferred hrtimer rearming")
> Reported-by: "Verma, Vishal L" <vishal.l.verma@intel.com>
> Closes: https://lore.kernel.org/r/70cd3e97fbb796e2eb2ff8cd4b7614ada05a5f24.camel%40intel.com
> Suggested-by: Thomas Gleixner <tglx@kernel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: "Verma, Vishal L" <vishal.l.verma@intel.com>

Tested-by: David Woodhouse <dwmw@amazon.co.uk>

I don't see this being merged yet?

Without this, Xen timer delivery (tested by the xen_shinfo_test KVM
selftest) is failing. I think the Fixes: tag is wrong though; it
actually broke with commit 15dd3a948855 ("hrtimer: Push reprogramming
timers into the interrupt return path"), didn't it?

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