This is a note to let you know that I've just added the patch titled iommu/vt-d: Serialize IOMMU GCMD register modifications to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: iommu-vt-d-serialize-iommu-gcmd-register-modificatio.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 331e2f956dbb1cffc87ca12905699501ba25c073 Author: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> Date: Fri Aug 28 08:06:15 2020 +0800 iommu/vt-d: Serialize IOMMU GCMD register modifications [ Upstream commit 6e4e9ec65078093165463c13d4eb92b3e8d7b2e8 ] 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 <baolu.lu@xxxxxxxxxxxxxxx> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> Cc: Kevin Tian <kevin.tian@xxxxxxxxx> Cc: Ashok Raj <ashok.raj@xxxxxxxxx> Link: https://lore.kernel.org/r/20200828000615.8281-1-baolu.lu@xxxxxxxxxxxxxxx Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c index 15a4ad31c510a..9d2d03545bb07 100644 --- a/drivers/iommu/intel_irq_remapping.c +++ b/drivers/iommu/intel_irq_remapping.c @@ -479,12 +479,18 @@ 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