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    SubjectRe: [PATCH v2 3/3] arm64: cpufeature: Change 32-bit EL0 to display enabled cores
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    Hi,

    On 10/17/23 13:01, Marc Zyngier wrote:
    > On Tue, 17 Oct 2023 06:23:22 +0100,
    > Jeremy Linton <jeremy.linton@arm.com> wrote:
    >>
    >> Now that we have the ability to display the list of cores
    >> with a feature when it is selectivly enabled, lets display the
    >> cores enabled for 32-bit use at EL0.
    >>
    >> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
    >> ---
    >> arch/arm64/kernel/cpufeature.c | 15 +++++++++++++--
    >> 1 file changed, 13 insertions(+), 2 deletions(-)
    >>
    >> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
    >> index b7b67bac0e60..512cbe446b41 100644
    >> --- a/arch/arm64/kernel/cpufeature.c
    >> +++ b/arch/arm64/kernel/cpufeature.c
    >> @@ -1533,8 +1533,17 @@ static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope)
    >> if (!has_cpuid_feature(entry, scope))
    >> return allow_mismatched_32bit_el0;
    >>
    >> - if (scope == SCOPE_SYSTEM)
    >> - pr_info("detected: 32-bit EL0 Support\n");
    >> + if (scope == SCOPE_SYSTEM) {
    >> + struct arm64_cpu_capabilities *has_32bit;
    >> +
    >> + has_32bit = (struct arm64_cpu_capabilities *)entry;
    >> +
    >> + has_32bit->cpus = system_32bit_el0_cpumask();
    >
    > This seems rather dodgy. 'entry' comes from a static const array which
    > will, in all likelihood be mapped R/O pretty soon after the initial
    > CPU bringup. Try offlining/onlining a CPU and you should see a
    > firework similar to what I have below (I hacked the CnP property, but
    > that's no different from what you are doing):

    Yes, dodgy is a good word. The other choices, maintain a mask just for
    the print or dump the static key and always use the cpu_32bit_el0_mask
    or some combination, weren't much better in the "ick" category. If
    anyone sees a better way I'm open to suggestion, although simply
    dropping this last patch is fine too.

    >
    > bash-5.1# echo 0 >/sys/devices/system/cpu/cpu2/online
    > [ 51.367137] psci: CPU2 killed (polled 0 ms)
    > bash-5.1# echo 1 >/sys/devices/system/cpu/cpu2/online
    > [ 56.703092] Unable to handle kernel write to read-only memory at virtual address ffff800080d63db0
    > [ 56.703494] Mem abort info:
    > [ 56.703627] ESR = 0x000000009600004f
    > [ 56.703799] EC = 0x25: DABT (current EL), IL = 32 bits
    > [ 56.704052] SET = 0, FnV = 0
    > [ 56.704196] EA = 0, S1PTW = 0
    > [ 56.704340] FSC = 0x0f: level 3 permission fault
    > [ 56.704575] Data abort info:
    > [ 56.704715] ISV = 0, ISS = 0x0000004f, ISS2 = 0x00000000
    > [ 56.704961] CM = 0, WnR = 1, TnD = 0, TagAccess = 0
    > [ 56.705195] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
    > [ 56.705435] swapper pgtable: 4k pages, 48-bit VAs, pgdp=000000008142e000
    > [ 56.705742] [ffff800080d63db0] pgd=10000000dbfff003, p4d=10000000dbfff003, pud=10000000dbffe003, pmd=10000000dbffc003, pte=0060000080d63783
    > [ 56.706310] Internal error: Oops: 000000009600004f [#1] PREEMPT SMP
    > [ 56.706591] Modules linked in:
    > [ 56.706741] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 6.6.0-rc1-00007-g805cc7d30885-dirty #1702
    > [ 56.707145] Hardware name: linux,dummy-virt (DT)
    > [ 56.707359] pstate: 800001c5 (Nzcv dAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
    > [ 56.707676] pc : cpu_enable_cnp+0x24/0x60
    > [ 56.707873] lr : verify_local_cpu_caps+0x6c/0x140
    > [ 56.708046] sp : ffff800082103e10
    > [ 56.708201] x29: ffff800082103e10 x28: 0000000000000000 x27: 0000000000000000
    > [ 56.708517] x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
    > [ 56.708837] x23: ffff800081eec540 x22: 0000000000000003 x21: ffff8000813945f0
    > [ 56.709166] x20: ffff800081394358 x19: ffff800080d63db0 x18: 0000000000000000
    > [ 56.709488] x17: 000000040044ffff x16: 00500073b5503510 x15: 0000000000000000
    > [ 56.709805] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
    > [ 56.710100] x11: 0000000000000000 x10: 0000000000000000 x9 : ffff8000800273ac
    > [ 56.710416] x8 : ffff80008003b640 x7 : 0000000000000000 x6 : 0000000000000000
    > [ 56.710738] x5 : 0000000000000000 x4 : ffff800081394000 x3 : ffff800081394000
    > [ 56.711070] x2 : ffff800081241ef8 x1 : ffff800080027218 x0 : ffff800080d63db0
    > [ 56.711396] Call trace:
    > [ 56.711512] cpu_enable_cnp+0x24/0x60
    > [ 56.711684] verify_local_cpu_caps+0x6c/0x140
    > [ 56.711885] verify_local_cpu_capabilities+0x1c/0x198
    > [ 56.712112] check_local_cpu_capabilities+0x28/0x50
    > [ 56.712337] secondary_start_kernel+0xb4/0x1a0
    > [ 56.712546] __secondary_switched+0xb8/0xc0
    > [ 56.712739] Code: 910003fd b0009b63 d00090c2 913be042 (f9000002)
    > [ 56.713013] ---[ end trace 0000000000000000 ]---
    > [ 56.713224] Kernel panic - not syncing: Attempted to kill the idle task!
    > [ 56.713518] SMP: stopping secondary CPUs
    > [ 56.713752] Kernel Offset: disabled
    > [ 56.713908] CPU features: 0x00000000,50024d43,1947f723
    > [ 56.714144] Memory Limit: none
    > [ 56.714292] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
    >
    > Thanks,
    >
    > M.
    >

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