Hi Stephan, Stephan Gerhold <stephan@xxxxxxxxxxx> writes: > On Wed, Mar 27, 2024 at 11:29:09PM +0000, Caleb Connolly wrote: >> On 27/03/2024 21:06, Konrad Dybcio wrote: >> > On 27.03.2024 10:04 PM, Volodymyr Babchuk wrote: >> >> 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. >> > > FWIW: This old patch series from Stephen Boyd is closely related: > https://urldefense.com/v3/__https://lore.kernel.org/linux-arm-msm/20190910160903.65694-1-swboyd@xxxxxxxxxxxx/__;!!GF_29dbcQIUBPA!yGecMHGezwkDU9t7XATVTI80PNGjZdQV2xsYFTl6EhpMMsRf_7xryKx8mEVpmTwTcKMGaaWomtyvr05zFcmsf2Kk$ > [lore[.]kernel[.]org] > >> The main use case I have is to map the command-db memory region on >> Qualcomm devices with a read-only mapping. It's already a const marked >> pointer and the API returns const pointers as well, so this series >> makes sure that even stray writes can't modify the memory. > > Stephen, what was the end result of that patch series? Mapping the > cmd-db read-only sounds cleaner than trying to be lucky with the right > set of cache flags. > I checked the series, but I am afraid that I have no capacity to finish this. Will it be okay to move forward with my patch? I understand that this is not the best solution, but it is simple and it works. If this is fine, I'll send v2 with all comments addressed. -- WBR, Volodymyr
