From 6e4e9ec65078093165463c13d4eb92b3e8d7b2e8 Mon Sep 17 00:00:00 2001 From: Lu Baolu Date: Fri, 28 Aug 2020 08:06:15 +0800 Subject: [PATCH] iommu/vt-d: Serialize IOMMU GCMD register modifications The VT-d spec requires (10.4.4 Global Command Register, GCMD_REG General Description) that: If multiple control fields in this register need to be modified, software must serialize the modifications through multiple writes to this register. However, in irq_remapping.c, modifications of IRE and CFI are done in one write. We need to do two separate writes with STS checking after each. It also checks the status register before writing command register to avoid unnecessary register write. Fixes: af8d102f999a4 ("x86/intel/irq_remapping: Clean up x2apic opt-out security warning mess") Signed-off-by: Lu Baolu Reviewed-by: Kevin Tian Cc: Andy Lutomirski Cc: Jacob Pan Cc: Kevin Tian Cc: Ashok Raj Link: https://lore.kernel.org/r/20200828000615.8281-1-baolu.lu@linux.intel.com Signed-off-by: Joerg Roedel --- drivers/iommu/intel/irq_remapping.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c index 23583b0e66a5..8f4ce72570ce 100644 --- a/drivers/iommu/intel/irq_remapping.c +++ b/drivers/iommu/intel/irq_remapping.c @@ -508,12 +508,18 @@ static void iommu_enable_irq_remapping(struct intel_iommu *iommu) /* Enable interrupt-remapping */ iommu->gcmd |= DMA_GCMD_IRE; - iommu->gcmd &= ~DMA_GCMD_CFI; /* Block compatibility-format MSIs */ writel(iommu->gcmd, iommu->reg + DMAR_GCMD_REG); - IOMMU_WAIT_OP(iommu, DMAR_GSTS_REG, readl, (sts & DMA_GSTS_IRES), sts); + /* Block compatibility-format MSIs */ + if (sts & DMA_GSTS_CFIS) { + iommu->gcmd &= ~DMA_GCMD_CFI; + writel(iommu->gcmd, iommu->reg + DMAR_GCMD_REG); + IOMMU_WAIT_OP(iommu, DMAR_GSTS_REG, + readl, !(sts & DMA_GSTS_CFIS), sts); + } + /* * With CFI clear in the Global Command register, we should be * protected from dangerous (i.e. compatibility) interrupts