Messages in this thread Patch in this message | | | Date | Mon, 11 Oct 2021 10:38:18 +0100 | From | Mark Rutland <> | Subject | Re: [RFC PATCH] arch: ARM64: add isb before enable pan |
| |
Hi,
On Fri, Oct 08, 2021 at 04:34:12PM +0800, Zhaoyang Huang wrote: > On Fri, Oct 8, 2021 at 4:01 PM Will Deacon <will@kernel.org> wrote: > > On Fri, Oct 08, 2021 at 02:07:49PM +0800, Huangzhaoyang wrote: > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > > > set_pstate_pan failure is observed in an ARM64 system occasionaly on a reboot > > > test, which can be work around by a msleep on the sw context. We assume > > > suspicious on disorder of previous instr of disabling SW_PAN and add an isb here. > > > > > > PS: > > > The bootup test failed with a invalid TTBR1_EL1 that equals 0x34000000, which is > > > alike racing between on chip PAN and SW_PAN. > > > > Sorry, but I'm struggling to understand the problem here. Please could you > > explain it in more detail? > > > > - Why does a TTBR1_EL1 value of `0x34000000` indicate a race? > > - Can you explain the race that you think might be occurring? > > - Why does an ISB prevent the race? > Please find panic logs[1], related codes[2], sample of debug patch[3] > below. TTBR1_EL1 equals 0x34000000 when panic
Just to check, how do you know the value of TTBR1_EL1 was 0x34000000? That isn't in the log sample below -- was that from the output of show_pte(), an external debugger, or something else?
I'm assuming from the "(ptrval)" bits below that can't have been from show_pte().
> and can NOT be captured > by the debug patch during retest (all entrances that msr ttbr1_el1 are > under watch) which should work. Adding ISB here to prevent race on > TTBR1 from previous access of sysregs which can affect the msr > result(the test is still ongoing). Could the race be > ARM64_HAS_PAN(automated by core) and SW_PAN. > > [1] > [ 0.348000] [0: migration/0: 11] Synchronous External Abort: > level 1 (translation table walk) (0x96000055) at 0xffffffc000e06004 > [ 0.352000] [0: migration/0: 11] Internal error: : 96000055 > [#1] PREEMPT SMP > [ 0.352000] [0: migration/0: 11] Modules linked in: > [ 0.352000] [0: migration/0: 11] Process migration/0 (pid: > 11, stack limit = 0x (ptrval)) > [ 0.352000] [0: migration/0: 11] CPU: 0 PID: 11 Comm: > migration/0 Tainted: G S
Assuming I've read the `taint_flags` table correctly, that 'S' is `TAINT_CPU_OUT_OF_SPEC`, for which we should dump warnings for at boot time. The 'G' indicates the absence of proprietary modules.
Can you provide a full dmesg for a failed boot, please?
Have you made any changes to arch/arm64/kernel/cpufeature.c?
Are you able to test with a mainline kernel?
> 4.14.199-22631304-abA035FXXU0AUJ4_T4 #2 > > [ 0.352000] [0: migration/0: 11] Hardware name: Spreadtrum > UMS9230 1H10 SoC (DT) > [ 0.352000] [0: migration/0: 11] task: (ptrval) > task.stack: (ptrval) > [ 0.352000] [0: migration/0: 11] pc : patch_alternative+0x68/0x27c > [ 0.352000] [0: migration/0: 11] lr : > __apply_alternatives.llvm.7450387295891320208+0x60/0x160 > > [2] > __apply_alternatives > for() > patch_alternative <----panic here in the 2nd round of loop > after invoking flush_icache_range > flush_icache_range > > [3] > sub \tmp1, \tmp1, #SWAPPER_DIR_SIZE > + tst \tmp1, #0xffff80000000 // check ttbr1_el1 valid > + b.le .
What are you trying to detect for here? This is testing both the ASID and BADDR[47] bits, so I don;t understand the rationale.
Thanks, Mark.
> msr ttbr1_el1, \tmp1 // set reserved ASID > > > > > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > --- > > > arch/arm64/kernel/cpufeature.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > > > index efed283..3c0de0d 100644 > > > --- a/arch/arm64/kernel/cpufeature.c > > > +++ b/arch/arm64/kernel/cpufeature.c > > > @@ -1663,6 +1663,7 @@ static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused) > > > WARN_ON_ONCE(in_interrupt()); > > > > > > sysreg_clear_set(sctlr_el1, SCTLR_EL1_SPAN, 0); > > > + isb(); > > > set_pstate_pan(1); > > > > SCTLR_EL1.SPAN only affects the PAN behaviour on taking an exception, which > > is itself a context-synchronizing event, so I can't see why the ISB makes > > any difference here (at least, for the purposes of PAN). > > > > Thanks, > > > > Will
| |