iommu/amd: Fix IOMMU perf counter clobbering during init

init_iommu_perf_ctr() clobbers the register when it checks write access
to IOMMU perf counters and fails to restore when they are writable.

Add save and restore to fix it.

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Fixes: 30861ddc9cca4 ("perf/x86/amd: Add IOMMU Performance Counter resource management")
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index 568c523..483f7bc 100644 (file)
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -1655,27 +1655,39 @@ static int iommu_pc_get_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr,
 static void init_iommu_perf_ctr(struct amd_iommu *iommu)
 {
        struct pci_dev *pdev = iommu->dev;
-       u64 val = 0xabcd, val2 = 0;
+       u64 val = 0xabcd, val2 = 0, save_reg = 0;
 
        if (!iommu_feature(iommu, FEATURE_PC))
                return;
 
        amd_iommu_pc_present = true;
 
+       /* save the value to restore, if writable */
+       if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, false))
+               goto pc_false;
+
        /* Check if the performance counters can be written to */
        if ((iommu_pc_get_set_reg(iommu, 0, 0, 0, &val, true)) ||
            (iommu_pc_get_set_reg(iommu, 0, 0, 0, &val2, false)) ||
-           (val != val2)) {
-               pci_err(pdev, "Unable to write to IOMMU perf counter.\n");
-               amd_iommu_pc_present = false;
-               return;
-       }
+           (val != val2))
+               goto pc_false;
+
+       /* restore */
+       if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, true))
+               goto pc_false;
 
        pci_info(pdev, "IOMMU performance counters supported\n");
 
        val = readl(iommu->mmio_base + MMIO_CNTR_CONF_OFFSET);
        iommu->max_banks = (u8) ((val >> 12) & 0x3f);
        iommu->max_counters = (u8) ((val >> 7) & 0xf);
+
+       return;
+
+pc_false:
+       pci_err(pdev, "Unable to read/write to IOMMU perf counter.\n");
+       amd_iommu_pc_present = false;
+       return;
 }
 
 static ssize_t amd_iommu_show_cap(struct device *dev,