Re: [PATCH v9 0/5] Support x2APIC mode with TCG accelerator

[Joao Martins]

On 09/11/2023 14:10, Bui Quang Minh wrote:
> On 11/9/23 17:11, Santosh Shukla wrote:
>> On 10/24/2023 8:51 PM, Bui Quang Minh wrote:
>>> Hi everyone,
>>>
>>> This series implements x2APIC mode in userspace local APIC and the
>>> RDMSR/WRMSR helper to access x2APIC registers in x2APIC mode. Intel iommu
>>> and AMD iommu are adjusted to support x2APIC interrupt remapping. With this
>>> series, we can now boot Linux kernel into x2APIC mode with TCG accelerator
>>> using either Intel or AMD iommu.
>>>
>>> Testing to boot my own built Linux 6.3.0-rc2, the kernel successfully boot
>>> with enabled x2APIC and can enumerate CPU with APIC ID 257
>>>
>>> Using Intel IOMMU
>>>
>>> qemu/build/qemu-system-x86_64 \
>>>    -smp 2,maxcpus=260 \
>>>    -cpu qemu64,x2apic=on \
>>>    -machine q35 \
>>>    -device intel-iommu,intremap=on,eim=on \
>>>    -device qemu64-x86_64-cpu,x2apic=on,core-id=257,socket-id=0,thread-id=0 \
>>>    -m 2G \
>>>    -kernel $KERNEL_DIR \
>>>    -append "nokaslr console=ttyS0 root=/dev/sda earlyprintk=serial
>>> net.ifnames=0" \
>>>    -drive file=$IMAGE_DIR,format=raw \
>>>    -nographic \
>>>    -s
>>>
>>> Using AMD IOMMU
>>>
>>> qemu/build/qemu-system-x86_64 \
>>>    -smp 2,maxcpus=260 \
>>>    -cpu qemu64,x2apic=on \
>>>    -machine q35 \
>>>    -device amd-iommu,intremap=on,xtsup=on \
>>>    -device qemu64-x86_64-cpu,x2apic=on,core-id=257,socket-id=0,thread-id=0 \
>>>    -m 2G \
>>>    -kernel $KERNEL_DIR \
>>>    -append "nokaslr console=ttyS0 root=/dev/sda earlyprintk=serial
>>> net.ifnames=0" \
>>>    -drive file=$IMAGE_DIR,format=raw \
>>>    -nographic \
>>>    -s
>>>
>>> Testing the emulated userspace APIC with kvm-unit-tests, disable test
>>> device with this patch
>>>
>>> diff --git a/lib/x86/fwcfg.c b/lib/x86/fwcfg.c
>>> index 1734afb..f56fe1c 100644
>>> --- a/lib/x86/fwcfg.c
>>> +++ b/lib/x86/fwcfg.c
>>> @@ -27,6 +27,7 @@ static void read_cfg_override(void)
>>>
>>>          if ((str = getenv("TEST_DEVICE")))
>>>                  no_test_device = !atol(str);
>>> +       no_test_device = true;
>>>
>>>          if ((str = getenv("MEMLIMIT")))
>>>                  fw_override[FW_CFG_MAX_RAM] = atol(str) * 1024 * 1024;
>>>
>>> ~ env QEMU=/home/minh/Desktop/oss/qemu/build/qemu-system-x86_64 ACCEL=tcg \
>>> ./run_tests.sh -v -g apic
>>>
>>> TESTNAME=apic-split TIMEOUT=90s ACCEL=tcg ./x86/run x86/apic.flat -smp 2
>>> -cpu qemu64,+x2apic,+tsc-deadline -machine kernel_irqchip=split FAIL
>>> apic-split (54 tests, 8 unexpected failures, 1 skipped)
>>> TESTNAME=ioapic-split TIMEOUT=90s ACCEL=tcg ./x86/run x86/ioapic.flat -smp
>>> 1 -cpu qemu64 -machine kernel_irqchip=split PASS ioapic-split (19 tests)
>>> TESTNAME=x2apic TIMEOUT=30 ACCEL=tcg ./x86/run x86/apic.flat -smp 2 -cpu
>>> qemu64,+x2apic,+tsc-deadline FAIL x2apic (54 tests, 8 unexpected failures,
>>> 1 skipped) TESTNAME=xapic TIMEOUT=60 ACCEL=tcg ./x86/run x86/apic.flat -smp
>>> 2 -cpu qemu64,-x2apic,+tsc-deadline -machine pit=off FAIL xapic (43 tests,
>>> 6 unexpected failures, 2 skipped)
>>>
>>>    FAIL: apic_disable: *0xfee00030: 50014
>>>    FAIL: apic_disable: *0xfee00080: f0
>>>    FAIL: apic_disable: *0xfee00030: 50014
>>>    FAIL: apic_disable: *0xfee00080: f0
>>>    FAIL: apicbase: relocate apic
>>>
>>> These errors are because we don't disable MMIO region when switching to
>>> x2APIC and don't support relocate MMIO region yet. This is a problem
>>> because, MMIO region is the same for all CPUs, in order to support these we
>>> need to figure out how to allocate and manage different MMIO regions for
>>> each CPUs. This can be an improvement in the future.
>>>
>>>    FAIL: nmi-after-sti
>>>    FAIL: multiple nmi
>>>
>>> These errors are in the way we handle CPU_INTERRUPT_NMI in core TCG.
>>>
>>>    FAIL: TMCCT should stay at zero
>>>
>>> This error is related to APIC timer which should be addressed in separate
>>> patch.
>>>
>>> Version 9 changes,
>>
>> Hi Bui,
>>
>> I have tested v9 on EPYC-Genoa system with kvm acceleration mode on, I could
>> see > 255 vCPU for Linux and Windows Guest.
>>
>> Tested-by: Santosh Shukla <Santosh.Shukla@amd.com>
> 
> Hi Santosh,
> 
> With KVM enabled, you may be using the in kernel APIC from KVM not the 
> emulated
> APIC in userspace as in this series.
> 

Your XTSup code isn't necessarily userspace APIC specific. You can have
accel=kvm with split irqchip and things will still work. I suspect that's how
Santosh tested it.

        Joao