Hi Caleb, Caleb Connolly <caleb.connolly@xxxxxxxxxx> writes: > On 27/03/2024 21:06, Konrad Dybcio wrote: >> On 27.03.2024 10:04 PM, Volodymyr Babchuk wrote: >>> >>> Hi Konrad, >>> >>> Konrad Dybcio <konrad.dybcio@xxxxxxxxxx> writes: >>> >>>> On 27.03.2024 9:09 PM, 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. >>>>> >>>>> 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. >>>>> >>>>> I tested this on SA8155P with Xen. >>>>> >>>>> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx> >>>>> --- >>>> >>>> Interesting.. >>>> >>>> +Doug, Rob have you ever seen this on Chrome? (FYI, Volodymyr, chromebooks >>>> ship with no qcom hypervisor) >>> >>> Well, maybe I was wrong when called this thing "hypervisor". All I know >>> that it sits in hyp.mbn partition and all what it does is setup EL2 >>> before switching to EL1 and running UEFI. >>> >>> In my experiments I replaced contents of hyp.mbn with U-Boot, which gave >>> me access to EL2 and I was able to boot Xen and then Linux as Dom0. >> >> Yeah we're talking about the same thing. I was just curious whether >> the Chrome folks have heard of it, or whether they have any changes/ >> workarounds for it. > > Does Linux ever write to this region? Given that the Chromebooks don't > seem to have issues with this (we have a bunch of them in pmOS and I'd > be very very surprised if this was an issue there which nobody had tried > upstreaming before) I'd guess the significant difference here is between > booting Linux in EL2 (as Chromebooks do?) vs with Xen. It does not write, but I assume that direction is irrelevant in this case. AFAIK, CPU signals memory type to the bus for both reads and writes, just with different signals: ARCACHE[3:0] and AWCACHE[3:0]. > > Volodymyr: have you tried booting the kernel directly from U-Boot in > EL2? Can you confirm if this issues also happens then? Yes, behavior is exactly the same. It does not work with WB, but work with WC or WT. -- WBR, Volodymyr
