df6e78ba22
[ Upstream commit b5e86a95541cea737394a1da967df4cd4d8f7182 ]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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|---|---|---|
| .. | ||
| Kconfig | ||
| Makefile | ||
| cap_audit.c | ||
| cap_audit.h | ||
| debugfs.c | ||
| dmar.c | ||
| iommu.c | ||
| irq_remapping.c | ||
| pasid.c | ||
| pasid.h | ||
| perf.c | ||
| perf.h | ||
| svm.c | ||
| trace.c | ||