iommu/vt-d: Clear PPR bit to ensure we get more page request interrupts

According to the VT-d specification we need to clear the PPR bit in
the Page Request Status register when handling page requests, or the
hardware won't generate any more interrupts.

This wasn't actually necessary on SKL/KBL (which may well be the
subject of a hardware erratum, although it's harmless enough). But
other implementations do appear to get it right, and we only ever get
one interrupt unless we clear the PPR bit.

Reported-by: CQ Tang <cq.tang@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: stable@vger.kernel.org

diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
index 97a818992d6ddcd16d62d29db693b131445cd0b7..d9939fa9b58887567d1fe8a7a94c7e5f1452cdf0 100644 (file)
--- a/drivers/iommu/intel-svm.c
+++ b/drivers/iommu/intel-svm.c
@@ -524,6 +524,10 @@ static irqreturn_t prq_event_thread(int irq, void *d)
        struct intel_svm *svm = NULL;
        int head, tail, handled = 0;
 
+       /* Clear PPR bit before reading head/tail registers, to
+        * ensure that we get a new interrupt if needed. */
+       writel(DMA_PRS_PPR, iommu->reg + DMAR_PRS_REG);
+
        tail = dmar_readq(iommu->reg + DMAR_PQT_REG) & PRQ_RING_MASK;
        head = dmar_readq(iommu->reg + DMAR_PQH_REG) & PRQ_RING_MASK;
        while (head != tail) {

diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index 821273ca4873b147136f46f235d83b344b192373..2d9b650047a5b96582f66dff2b2581cce97c2b65 100644 (file)
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -235,6 +235,9 @@ static inline void dmar_writeq(void __iomem *addr, u64 val)
 /* low 64 bit */
 #define dma_frcd_page_addr(d) (d & (((u64)-1) << PAGE_SHIFT))
 
+/* PRS_REG */
+#define DMA_PRS_PPR    ((u32)1)
+
 #define IOMMU_WAIT_OP(iommu, offset, op, cond, sts)                    \
 do {                                                                   \
        cycles_t start_time = get_cycles();                             \