> From: Lu Baolu <baolu...@linux.intel.com>
> Sent: Thursday, August 27, 2020 12:25 PM
>
> 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.
>
> 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 | 11 +++++++++--
> 1 file changed, 9 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)
>
> diff --git a/drivers/iommu/intel/irq_remapping.c
> b/drivers/iommu/intel/irq_remapping.c
> index 9564d23d094f..7552bb7e92c8 100644
> --- a/drivers/iommu/intel/irq_remapping.c
> +++ b/drivers/iommu/intel/irq_remapping.c
> @@ -507,12 +507,19 @@ 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 */
> + sts = readl(iommu->reg + DMAR_GSTS_REG);
no need of this readl as the status is already three in IOMMU_WAIT_OP.
> + 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
