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") Cc: Andy Lutomirski <l...@amacapital.net> Cc: Jacob Pan <jacob.jun....@linux.intel.com> Cc: Kevin Tian <kevin.t...@intel.com> Cc: Ashok Raj <ashok....@intel.com> Signed-off-by: Lu Baolu <baolu...@linux.intel.com> --- drivers/iommu/intel/irq_remapping.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) Change log: v1->v2: - v1 posted here https://lore.kernel.org/linux-iommu/20200826025825.2322-1-baolu...@linux.intel.com/ - Add status check before disabling CFI (Kevin) v2->v3: - v2 posted here https://lore.kernel.org/linux-iommu/20200827042513.30292-1-baolu...@linux.intel.com/ - Remove unnecessary register read (Kevin) diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c index 9564d23d094f..a91dd997d268 100644 --- a/drivers/iommu/intel/irq_remapping.c +++ b/drivers/iommu/intel/irq_remapping.c @@ -507,12 +507,18 @@ 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 -- 2.17.1