Re: [Xen-devel] [PATCH v3 for 4.10] x86/vpt: guarantee the return value of pt_update_irq() set in vIRR or PIR

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi,

On 20/10/17 15:16, Jan Beulich wrote:
> > > > On 20.10.17 at 15:23, <julien.grall@xxxxxxxxxx> wrote:
> > On 20/10/17 12:42, Jan Beulich wrote:
> > > > > > On 20.10.17 at 02:35, <chao.gao@xxxxxxxxx> wrote:
> > > > pt_update_irq() is expected to return the vector number of periodic
> > > > timer interrupt, which should be set in vIRR of vlapic or in PIR.
> > > > Otherwise it would trigger the assertion in vmx_intr_assist(), please
> > > > seeing
> > > > https://lists.xenproject.org/archives/html/xen-devel/2017-10/msg00915.html.
> > > >
> > > > But it fails to achieve that in the following two case:
> > > > 1. hvm_isa_irq_assert() may not set the corresponding bit in vIRR for
> > > > mask field of IOAPIC RTE is set. Please refer to the call tree
> > > > vmx_intr_assist() -> pt_update_irq() -> hvm_isa_irq_assert() ->
> > > > assert_irq() -> assert_gsi() -> vioapic_irq_positive_edge(). The patch
> > > > checks whether the vector is set or not in vIRR of vlapic or PIR before
> > > > returning.
> > > >
> > > > 2. someone changes the vector field of IOAPIC RTE between asserting
> > > > the irq and getting the vector of the irq, leading to setting the
> > > > old vector number but returning a different vector number. This patch
> > > > allows hvm_isa_irq_assert() to accept a callback which can get the
> > > > interrupt vector with irq_lock held. Thus, no one can change the vector
> > > > between the two operations.
> > > >
> > > > BTW, the first argument of pi_test_and_set_pir() should be uint8_t
> > > > and I take this chance to fix it.
> > > >
> > > > Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> > > Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> > Do you have any opinion on this patch going to Xen 4.10?
> Well, the author having hopes that this addresses the assertion
> failure we keep seeing in osstest every once in a while, I think
> we certainly want to have it despite me not being fully convinced
> that it'll actually help. I'm sufficiently convinced though it won't do
> any bad.
I guess it is worth having a try then:

Release-acked-by: Julien Grall <julien.grall@xxxxxxxxxx>

Cheers,

--
Julien Grall

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