On 11/09/20 13:52, Will Deacon wrote: > On Fri, Nov 06, 2020 at 02:48:35PM +0000, Qais Yousef wrote: > > On 11/06/20 13:00, Will Deacon wrote: > > > On Fri, Nov 06, 2020 at 12:54:25PM +0000, Qais Yousef wrote: > > > > FWIW I have my v3 over here in case it's of any help. It solves the problem of > > > > HWCAP discovery when late AArch32 CPU is booted by populating boot_cpu_date > > > > with 32bit features then. > > > > > > > > git clone https://git.gitlab.arm.com/linux-arm/linux-qy.git -b asym-aarch32-upstream-v3 origin/asym-aarch32-upstream-v3 > > > > > > Cheers, I've done something similar. I was hoping to post it today, but I've > > > been side-tracked with bug fixing this morning. The main headache I ended up > > > with was allowing late-onlining of 64-bit-only CPUs if all the boot CPUs > > > are 32-bit capable. What do you do in that case? > > > > Do you mean if CPUs 0-3 were 32bit capable and we boot with maxcpus=4 then > > attempt to bring the remaining 64bit-only cpus online later? > > Right. I think we will refuse to online them. I'll post my attempt at > handling that shortly. Sorry for the delayed response. You're right, I tried that and they refuse to come online. We missed that tbh. Haven't thought what we should do yet. I tried your v2 and it failed similarly. I usually have a similar hunk in my testing to check how the kernel perceives the 32bit support when I execute a binary: diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index f447d313a9c5..a9549e55a6c8 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -611,6 +611,9 @@ static inline bool system_supports_32bit_el0(void) { u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1); + pr_err("System supports symmetric 32bit el0: %d\n", id_aa64pfr0_32bit_el0(pfr0)); + pr_err("System supports Asymmetric 32bit el0: %ld\n", static_branch_unlikely(&arm64_mismatched_32bit_el0)); + return id_aa64pfr0_32bit_el0(pfr0) || static_branch_unlikely(&arm64_mismatched_32bit_el0); } In your v2 both conditions are true. In my series we see the system as symmetric if we boot the 32bit capable cpus _only_. > > Haven't tried that tbh. What symptoms do you expect to see? I can try it out. > > I'm off for the remainder of the day, but can spend few mins to run an > > experiment for sure. > > No probs; I've been taking Friday afternoons off to burn holiday anyway, so > you didn't miss anything! :-) Thanks -- Qais Yousef
