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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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