On 16/02/2023 10:00, Joerg Roedel wrote:
> Missing Signed-off-by.
>
Not really missing it. It's actually there, right after the 'Fixes' tag.
> Also adding Vasant from AMD for review.
>
FWIW, I think I have a better version that handles better the bullet (2) further
below. But I'm still testing it.
> On Wed, Feb 08, 2023 at 01:19:38PM +0000, Joao Martins wrote:
>> On KVM GSI routing table updates, specially those where they have vIOMMUs
>> with interrupt remapping enabled (e.g. to boot >255vcpus guests without
>> relying on KVM_FEATURE_MSI_EXT_DEST_ID), a VMM may update the backing VF
>> MSIs with new VCPU affinities.
>>
>> On AMD this translates to calls to amd_ir_set_vcpu_affinity() and
>> eventually to amd_iommu_{de}activate_guest_mode() with a new GATag
>> outlining the VM ID and (new) VCPU ID. On vCPU blocking and unblocking
>> paths it disables AVIC, and rely on GALog to convey the wakeups to any
>> sleeping vCPUs. KVM will store a list of GA-mode IR entries to each
>> running/blocked vCPU. So any vCPU Affinity update to a VF interrupt happen
>> via KVM, and it will change already-configured-guest-mode IRTEs with a new
>> GATag.
>>
>> The issue is that amd_iommu_activate_guest_mode() will essentially only
>> change IRTE fields on transitions from non-guest-mode to guest-mode and
>> otherwise returns *with no changes to IRTE* on already configured
>> guest-mode interrupts. To the guest this means that the VF interrupts
>> remain affined to the first vCPU these were first configured, and guest
>> will be unable to either VF interrupts and receive messages like this from
>> spurious interrupts (e.g. from waking the wrong vCPU in GALog):
>>
>> [ 167.759472] __common_interrupt: 3.34 No irq handler for vector
>> [ 230.680927] mlx5_core 0000:00:02.0: mlx5_cmd_eq_recover:247:(pid
>> 3122): Recovered 1 EQEs on cmd_eq
>> [ 230.681799] mlx5_core 0000:00:02.0:
>> wait_func_handle_exec_timeout:1113:(pid 3122): cmd[0]: CREATE_CQ(0x400)
>> recovered after timeout
>> [ 230.683266] __common_interrupt: 3.34 No irq handler for vector
>>
>> Given that amd_ir_set_vcpu_affinity() uses amd_iommu_activate_guest_mode()
>> underneath it essentially means that VCPU affinity changes of IRTEs are
>> nops if it was called once for the IRTE already (on VMENTER). Fix it by
>> dropping the check for guest-mode at amd_iommu_activate_guest_mode(). Same
>> thing is applicable to amd_iommu_deactivate_guest_mode() although, even if
>> the IRTE doesn't change underlying DestID on the host, the VFIO IRQ handler
>> will still be able to poke at the right guest-vCPU.
>>
>> Fixes: b9c6ff94e43a ("iommu/amd: Re-factor guest virtual APIC (de-)activation code")
>> Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
>> ---
>> Some notes in other related flaws as I looked at this:
>>
>> 1) amd_iommu_deactivate_guest_mode() suffers from the same issue as this patch,
>> but it should only matter for the case where you rely on irqbalance-like
>> daemons balancing VFIO IRQs in the hypervisor. Though, it doesn't translate
>> into guest failures, more like performance "misdirection". Happy to fix it, if
>> folks also deem it as a problem.
>>
>> 2) This patch doesn't attempt at changing semantics around what
>> amd_iommu_activate_guest_mode() has been doing for a long time [since v5.4]
>> (i.e. clear the whole IRTE and then changes its fields). As such when
>> updating the IRTEs the interrupts get isRunning and DestId cleared, thus
>> we rely on the GALog to inject IRQs into vCPUs /until/ the vCPUs block
>> and unblock again (which is when they update the IOMMU affinity), or the
>> AVIC gets momentarily disabled. I have patches that improve this part as a
>> follow-up, but I thought that this patch had value on its own onto fixing
>> what has been broken since v5.4 ... and that it could be easily carried
>> to stable trees.
>>
>> ---
>> drivers/iommu/amd/iommu.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
>> index cbeaab55c0db..afe1f35a4dd9 100644
>> --- a/drivers/iommu/amd/iommu.c
>> +++ b/drivers/iommu/amd/iommu.c
>> @@ -3476,7 +3476,7 @@ int amd_iommu_activate_guest_mode(void *data)
>> u64 valid;
>>
>> if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
>> - !entry || entry->lo.fields_vapic.guest_mode)
>> + !entry)
>> return 0;
>>
>> valid = entry->lo.fields_vapic.valid;
>> --
>> 2.17.2
>>
