Re: [Qemu-devel] [PATCH v2] pc: Fix and clean up PIC-to-APIC IRQ path

[Jan Kiszka]

On 2011-09-03 10:58, Blue Swirl wrote:
> On Thu, Sep 1, 2011 at 9:08 AM, Jan Kiszka <address@hidden> wrote:
>> The master PIC is connected to the LINTIN0 of the APICs. As the APIC
>> currently does not track the state of that line, we have to ask the PIC
>> to reinject its IRQ after the CPU picked up an event from the APIC.
>>
>> This introduces pic_get_output to read the master PIC IRQ line state
>> without changing it. The APIC uses this function to decide if a PIC IRQ
>> should be reinjected on apic_update_irq. This reflects better how the
>> real hardware works.
>>
>> The patch fixes some failures of the kvm unit tests apic and eventinj by
>> allowing to enable the proper CPU IRQ deassertion when the guest masks
>> some pending IRQs at PIC level.
>>
>> Signed-off-by: Jan Kiszka <address@hidden>
>> ---
>>
>> Changes in v2:
>>  - Avoid adding pic_level to the APIC state, obtain PIC output via
>>   pic_get_level instead
>>  - Do not reassert PIC interrupt if APIC is not accepting it
>>  - Use apic_deliver_pic_intr for reassertion to ensure correct
>>   processing
>>
>> This is not as nice as the previous version /wrt the interaction of PIC
>> and APIC. But it avoids breaking the APIC vmstate for the sake of
>> internal changes, also keeping it compatible with the upcoming KVM
>> in-kernel APIC (that allows no easy pic_level state extraction). The
>> interconnection between PIC and APIC may look nicer in the future with
>> QOM. And in the end this just reflects the "beauty" of the x86
>> architecture.
>>
>>  hw/apic.c  |    4 ++++
>>  hw/i8259.c |   15 +++++++--------
>>  hw/pc.c    |    3 ---
>>  hw/pc.h    |    2 +-
>>  4 files changed, 12 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/apic.c b/hw/apic.c
>> index d8f56c8..8289eef 100644
>> --- a/hw/apic.c
>> +++ b/hw/apic.c
>> @@ -23,6 +23,7 @@
>>  #include "host-utils.h"
>>  #include "sysbus.h"
>>  #include "trace.h"
>> +#include "pc.h"
>>
>>  /* APIC Local Vector Table */
>>  #define APIC_LVT_TIMER   0
>> @@ -399,6 +400,9 @@ static void apic_update_irq(APICState *s)
>>     }
>>     if (apic_irq_pending(s) > 0) {
>>         cpu_interrupt(s->cpu_env, CPU_INTERRUPT_HARD);
>> +    } else if (apic_accept_pic_intr(&s->busdev.qdev) &&
>> +               pic_get_output(isa_pic)) {
> 
> This is indeed ugly. Why doesn't APIC track PIC output?

For the reasons explained above.

Jan

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