From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Lu Baolu <baolu.lu@linux.intel.com>,
        Kevin Tian <kevin.tian@intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Joerg Roedel <jroedel@suse.de>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.8 110/186] iommu/vt-d: Serialize IOMMU GCMD register modifications
Date:   Tue,  8 Sep 2020 17:24:12 +0200
Message-Id: <20200908152246.966312595@linuxfoundation.org>
In-Reply-To: <20200908152241.646390211@linuxfoundation.org>
References: <20200908152241.646390211@linuxfoundation.org>
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From: Lu Baolu <baolu.lu@linux.intel.com>

[ 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@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Link: https://lore.kernel.org/r/20200828000615.8281-1-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 aa096b333a991..4828f4fe09ab5 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
-- 
2.25.1