Hi Maulik "Maulik Shah (mkshah)" <quic_mkshah@xxxxxxxxxxx> writes: > On 3/28/2024 1:39 AM, Volodymyr Babchuk wrote: >> It appears that hardware does not like cacheable accesses to this >> region. Trying to access this shared memory region as Normal Memory >> leads to secure interrupt which causes an endless loop somewhere in >> Trust Zone. > > Linux does not write into cmd-db region. This region is write > protected by XPU. Making this region uncached magically solves the XPU > write fault > issue. > > Can you please include above details? Sure, I'll add this to the next version. >> The only reason it is working right now is because Qualcomm >> Hypervisor >> maps the same region as Non-Cacheable memory in Stage 2 translation >> tables. The issue manifests if we want to use another hypervisor (like >> Xen or KVM), which does not know anything about those specific >> mappings. This patch fixes the issue by mapping the shared memory as >> Write-Through. This removes dependency on correct mappings in Stage 2 >> tables. > > Using MEMREMAP_WC also resolves for qcm6490, see below comment. > >> I tested this on SA8155P with Xen. >> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx> >> --- >> drivers/soc/qcom/cmd-db.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c >> index a5fd68411bed5..dd5ababdb476c 100644 >> --- a/drivers/soc/qcom/cmd-db.c >> +++ b/drivers/soc/qcom/cmd-db.c >> @@ -324,7 +324,7 @@ static int cmd_db_dev_probe(struct platform_device *pdev) >> return -EINVAL; >> } >> - cmd_db_header = memremap(rmem->base, rmem->size, MEMREMAP_WB); >> + cmd_db_header = memremap(rmem->base, rmem->size, MEMREMAP_WT); > > In downstream, we have below which resolved similar issue on qcm6490. > > cmd_db_header = memremap(rmem->base, rmem->size, MEMREMAP_WC); > > Downstream SA8155P also have MEMREMAP_WC. Can you please give it a try > on your device? Yes, MEMREMAP_WC works as well. This opens the question: which type is more correct? I have no deep understanding in QCOM internals so it is hard to me to answer this question. -- WBR, Volodymyr
