[PATCH v2] iommu: amd: Fix IOMMU perf counter clobbering during init

Shuah Khan
2020-01-23T22:32:18Z

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>
---
Changes since v1:
-- Fix bug in sucessful return path. Add a return instead of
fall through to pc_false error case

drivers/iommu/amd_iommu_init.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index 568c52317757..483f7bc379fa 100644
--- 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,
--
2.20.1