Hi Tyler, On 11/07/2019 05:14, Tyler Baicar OS wrote: > On Tue, Jul 9, 2019 at 8:52 PM Tyler Baicar OS <baicar@xxxxxxxxxxxxxxxxxxxxxx> wrote: >> On Mon, Jul 8, 2019 at 10:10 AM James Morse <james.morse@xxxxxxx> wrote: >>> On 02/07/2019 17:51, Tyler Baicar OS wrote: >>>> @@ -632,6 +633,8 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) >>>> >>>> inf = esr_to_fault_info(esr); >>>> >>>> + arch_arm_ras_report_error(); >>>> + >>>> /* >>>> * Return value ignored as we rely on signal merging. >>>> * Future patches will make this more robust. >>>> >>> >>> If we interrupted a preemptible context, do_sea() is preemptible too... This means we >>> can't know if we're still running on the same CPU as the one that took the external-abort. >>> (until this series, it hasn't mattered). >>> >>> Fixing this means cramming something into entry.S's el1_da, as this may unmask interrupts >>> before calling do_mem_abort(). But its going to be ugly because some of do_mem_abort()s >>> ESR values need to be preemptible because they sleep, e.g. page-faults calling >>> handle_mm_fault(). >>> For do_sea(), do_exit() will 'fix' the preempt count if we kill the thread, but if we >>> don't, it still needs to be balanced. Doing all this in assembly is going to be unreadable! >>> >>> Mark Rutland has a series to move the entry assembly into C [0]. Based on that that it >>> should be possible for the new el1_abort() to spot a Synchronous-External-Abort ESR, and >>> wrap the do_mem_abort() with preempt enable/disable, before inheriting the flags. (which >>> for synchronous exceptions, I think we should always do) >>> >>> [0] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/entry-deasm >> Good catch! I didn't think the synchronous route was preemptible. >> I wasn't seeing this issue when testing this on emulation, but I was able to >> test and prove the issue on a Neoverse N1 SDP: >> >> root@genericarmv8:~# echo 0x100000000 > /proc/cached_read >> [ 42.985622] Reading from address 0x100000000 >> [ 42.989893] WARNING: CPU: 0 PID: 2812 at /home/tyler/neoverse/arm-reference- >> platforms/linux/arch/arm64/kernel/cpufeature.c:1940 this_cpu_has_cap+0x68/0x78 [...] >> [ 43.175647] Internal error: synchronous external abort: 96000410 [#1] >> PREEMPT SMP [...] >> I'll pull Mark's series in and add the preempt enable/disable around the call >> to do_mem_abort() in el1_abort() and test that out! > > I was able to pull in the series mentioned [0] and add a patch to wrap > do_mem_abort with preempt disable/enable and the warning has gone away. Great. I spoke to Mark who commented he hadn't had the time to finish rebasing it onto for-next/core. (which I guess is why it didn't get posted!). I've taken a stab at picking out the 'synchronous' parts and rebasing it onto arm64's for-next/core. That tree is here: http://www.linux-arm.org/git?p=linux-jm.git;a=shortlog;h=refs/heads/deasm_sync_only/v0 (this should save you doing the rebase) I'll aim to rebase/retest and post it next week. > diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c > index 43aa78331e72..26cdf7db511a 100644 > --- a/arch/arm64/kernel/entry-common.c > +++ b/arch/arm64/kernel/entry-common.c > @@ -118,7 +118,25 @@ static void el1_abort(struct pt_regs *regs, unsigned long esr) el0_ia/da will have the same problem. > unsigned long far = read_sysreg(far_el1); > local_daif_inherit(regs); > far = untagged_addr(far); > - do_mem_abort(far, esr, regs); > + > + switch (esr & ESR_ELx_FSC) { > + case ESR_ELx_FSC_EXTABT: // Synchronous External Abort > + case 0x14: // SEA level 0 translation table walk > + case 0x15: // SEA level 1 translation table walk > + case 0x16: // SEA level 2 translation table walk > + case 0x17: // SEA level 3 translation table walk > + case 0x18: // Synchronous ECC error > + case 0x1c: // SECC level 0 translation table walk > + case 0x1d: // SECC level 1 translation table walk > + case 0x1e: // SECC level 2 translation table walk > + case 0x1f: // SECC level 3 translation table walk Hex numbers, lovely. KVM has a helper for this, can we move/clean that so we can use it here? > + preempt_disable(); This is still too late. You can take an interrupt between local_daif_inherit() and be migrated, before you call preempt_disable() here. The local_daif_inherit() may need to move into the switch() too. It may be simpler to fold the 'is_extabt(esr)' check into el1_sync, so that these bypass el1_abort() and call do_sea() directly, which could then handle the far-read, preempt-count and daif-inherit itself. I prefer ... whichever looks cleanest! > + do_mem_abort(far, esr, regs); > + preempt_enable(); > + break; > + default: > + do_mem_abort(far, esr, regs); > + }; > } Thanks, James
