> On Apr 15, 2019, at 12:37 PM, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote:
>
> On Mon, Apr 15, 2019 at 12:12:58PM -0700, Nadav Amit wrote:
>>> On Apr 15, 2019, at 12:09 PM, Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
>>>
>>>> On Apr 15, 2019, at 12:00 PM, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote:
>>>>
>>>> On Mon, Apr 15, 2019 at 11:31:00AM -0700, nadav.amit@xxxxxxxxx wrote:
>>>>> From: Nadav Amit <nadav.amit@xxxxxxxxx>
>>>>>
>>>>> test_enable_x2apic() unintentionally changes the APIC base address to
>>>>> zero and resets the BSP indication. This actually causes the local APIC
>>>>> to overlap the IDT area, which is wrong. Prevent it from happening by
>>>>> keeping the APIC base address and BSP-bit as it was before.
>>>>>
>>>>> Signed-off-by: Nadav Amit <nadav.amit@xxxxxxxxx>
>>>>> ---
>>>>> x86/apic.c | 4 ++--
>>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/x86/apic.c b/x86/apic.c
>>>>> index 51744cf..0849f87 100644
>>>>> --- a/x86/apic.c
>>>>> +++ b/x86/apic.c
>>>>> @@ -90,11 +90,11 @@ static void test_enable_x2apic(void)
>>>>> report("disabled to x2apic enabled",
>>>>> test_write_apicbase_exception(APIC_EN | APIC_EXTD));
>>>>>
>>>>> - wrmsr(MSR_IA32_APICBASE, APIC_EN);
>>>>> + wrmsr(MSR_IA32_APICBASE, APIC_EN | APIC_DEFAULT_PHYS_BASE | APIC_BSP);
>>>>> report("apic enabled to invalid state",
>>>>> test_write_apicbase_exception(APIC_EXTD));
>>>>>
>>>>> - wrmsr(MSR_IA32_APICBASE, APIC_EN | APIC_EXTD);
>>>>> + wrmsr(MSR_IA32_APICBASE, APIC_EN | APIC_EXTD | APIC_DEFAULT_PHYS_BASE | APIC_BSP);
>>>>
>>>> It probably doesn't matter since AFAIK kvm-unit-tests always uses the
>>>> default base, but preserving the current base+BSP would be preferred.
>>>> The #GP tests get away with using APIC_DEFAULT_PHYS_BASE because the
>>>> WRMSR will never succeed, but even that is poor form. And the test
>>>> should also reset to xAPIC when it's done.
>>>>
>>>> I think the attached patch covers everything.
>>>
>>> Thanks. The base is indeed the default, so it should not matter, but your
>>> change should make the code more robust.
>>>
>>> One important comment regarding your patch:
>>>
>>>> + if (!(orig_apicbase & APIC_EXTD))
>>>> + reset_apic();
>>>
>>> This is not needed, since enable_x2apic() will only return true if it
>>> succeeded in enabling x2apic. In addition, this is wrong, since reset_apic()
>>> should (usually, and specifically in this case) be followed with:
>>>
>>> apic_write(APIC_SPIV, 0x1ff);
>>>
>>> And not the other way around (there are actually a couple of missing writes
>>> to software-enable the APIC after reset_apic(), which I’ll send later).
>>
>> Correcting myself - I understand (now) that you want to reset back to xapic, so
>> that’s fine. Just keep "apic_write(APIC_SPIV, 0x1ff);” after the reset, please.
>
> Ah, will do, I glazed over the apic_write() and didn't consider its purpose.
Sorry for not being consistent, but actually the apic_reset() seems wrong in
general.
enable_x2apic() is used in the context of test_enable_x2apic() to figure out
whether x2apic was enabled before. It is actually initially enabled after
boot (see cstart64.S). So disabling it here would not be appropriate.
