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

[Sean Christopherson <seanjc@google.com>]

On Mon, May 11, 2026, David Woodhouse wrote:
> 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: Vishal L Verma <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: Vishal L Verma <vishal.l.verma@intel.com>
> 
> Tested-by: David Woodhouse <dwmw@amazon.co.uk>

Tested-by: Sean Christopherson <seanjc@google.com>

> I don't see this being merged yet?
> 
> Without this, Xen timer delivery (tested by the xen_shinfo_test KVM
> selftest) is failing.

And many, many other issues with KVM.  I.e. we need this or something like it
in 7.1.