When QEMU records an AMD-Vi event-log entry for an IO page fault, it
sets the event interrupt status bit and injects the event interrupt.
Linux kernel prior to commit 2379f3485239 ("iommu/amd: Refactor IOMMU
interrupt handling logic for Event, PPR, and GA logs") clears the status
register with a combined mask AMD_IOMMU_INT_MASK when handling any IOMMU
interrupt. That mask includes the
GA log interrupt (MMIO_STATUS_GALOG_INT_MASK) and
overflow (MMIO_STATUS_GALOG_OVERFLOW_MASK) bits, even when the interrupt
being handled is only an event-log interrupt.
QEMU does not produce GA log entries or set GA log status. However, the
emulated status register still accepts guest writes to the GA log status
bits as normal writes. As a result, a guest status clear write that
includes those bits can latch a spurious GA log overflow. The guest then
observes GA log status that QEMU did not generate and repeatedly
restarts the GA log.
The below guest dmesg logs are from v6.4 Linux kernel.
[ 57.818224] virtio-pci 0000:01:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT
domain=0x0000 address=0xc0000000 flags=0x0009]
[ 57.821130] virtio-pci 0000:01:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT
domain=0x0000 address=0xc0000000 flags=0x0009]
[ 57.824003] AMD-Vi: IOMMU GA Log overflow
[ 57.825099] AMD-Vi: IOMMU GA Log restarting
[ 57.826338] AMD-Vi: IOMMU GA Log overflow
[ 57.827425] AMD-Vi: IOMMU GA Log restarting
[ 57.828657] AMD-Vi: IOMMU GA Log overflow
[ 57.829758] AMD-Vi: IOMMU GA Log restarting
[ 57.830986] AMD-Vi: IOMMU GA Log overflow
[ 57.832063] AMD-Vi: IOMMU GA Log restarting
Mainline Linux commit 2379f3485239 ("iommu/amd: Refactor IOMMU interrupt
handling logic for Event, PPR, and GA logs") avoids triggering this by
chance by clearing only the status bits for the log being handled. However,
older guests still use the combined clear mask.
Add the GA log interrupt and overflow bits to the AMDVI_MMIO_STATUS
w1cmask so guest writes cannot create unsupported GA log status. This
does not implement GA log production. It only prevents guest status clear
writes from creating GA log status that QEMU did not generate to
emulated IO page fault for guest Linux kernel.
Fixes: 12499b23315b ("x86_iommu/amd: Enable Guest virtual APIC support")
Signed-off-by: Dongli Zhang <[email protected]>
---
v1->v2:
- As the previous commit replaced the hardcoded value 0x67 with a macro,
update the macro instead of the hardcoded value used by amdvi_init().
hw/i386/amd_iommu.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/hw/i386/amd_iommu.h b/hw/i386/amd_iommu.h
index 9cd510d790..4932568a0f 100644
--- a/hw/i386/amd_iommu.h
+++ b/hw/i386/amd_iommu.h
@@ -125,7 +125,8 @@
#define AMDVI_MMIO_STATUS_W1C_MASK \
(AMDVI_MMIO_STATUS_EVT_OVF | AMDVI_MMIO_STATUS_EVENT_INT | \
AMDVI_MMIO_STATUS_COMP_INT | AMDVI_MMIO_STATUS_PPR_OVF | \
- AMDVI_MMIO_STATUS_PPR_INT)
+ AMDVI_MMIO_STATUS_PPR_INT | AMDVI_MMIO_STATUS_GALOG_OVF | \
+ AMDVI_MMIO_STATUS_GALOG_INT)
#define AMDVI_CMDBUF_ID_BYTE 0x07
#define AMDVI_CMDBUF_ID_RSHIFT 4
--
2.39.3
