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| author | Jacob Pan <jacob.jun.pan@linux.intel.com> | 2024-07-02 15:08:33 +0200 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2024-07-03 17:39:25 +0200 |
| commit | b5e86a95541cea737394a1da967df4cd4d8f7182 (patch) | |
| tree | 3f5895605dcc0a9d13b333b7e42fb0837d13fe0d /drivers/iommu | |
| parent | iommu/vt-d: Use try_cmpxchg64() in intel_pasid_get_entry() (diff) | |
| download | linux-b5e86a95541cea737394a1da967df4cd4d8f7182.tar.xz linux-b5e86a95541cea737394a1da967df4cd4d8f7182.zip | |
iommu/vt-d: Handle volatile descriptor status read
Queued invalidation wait descriptor status is volatile in that IOMMU
hardware writes the data upon completion.
Use READ_ONCE() to prevent compiler optimizations which ensures memory
reads every time. As a side effect, READ_ONCE() also enforces strict
types and may add an extra instruction. But it should not have negative
performance impact since we use cpu_relax anyway and the extra time(by
adding an instruction) may allow IOMMU HW request cacheline ownership
easier.
e.g. gcc 12.3
BEFORE:
81 38 ad de 00 00 cmpl $0x2,(%rax)
AFTER (with READ_ONCE())
772f: 8b 00 mov (%rax),%eax
7731: 3d ad de 00 00 cmp $0x2,%eax
//status data is 32 bit
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20240607173817.3914600-1-jacob.jun.pan@linux.intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20240702130839.108139-2-baolu.lu@linux.intel.com
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'drivers/iommu')
| -rw-r--r-- | drivers/iommu/intel/dmar.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c index 304e84949ca7..1c8d3141cb55 100644 --- a/drivers/iommu/intel/dmar.c +++ b/drivers/iommu/intel/dmar.c @@ -1446,7 +1446,7 @@ restart: */ writel(qi->free_head << shift, iommu->reg + DMAR_IQT_REG); - while (qi->desc_status[wait_index] != QI_DONE) { + while (READ_ONCE(qi->desc_status[wait_index]) != QI_DONE) { /* * We will leave the interrupts disabled, to prevent interrupt * context to queue another cmd while a cmd is already submitted |