Messages in this thread | | | Date | Mon, 14 Jan 2019 11:30:16 +0000 | From | Hedi Berriche <> | Subject | Re: [PATCH 3/3] x86/platform/UV: use efi_runtime_sem to serialise BIOS calls |
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On Thu, Jan 10, 2019 at 07:14 Bhupesh Sharma wrote: >Hi Hedi,
Hi Bhupesh,
>Thanks for the patchset.
Thanks for looking at it.
>I will give this a go on my sgi-uv300 machine and come back with more >detailed inputs,
and for testing it.
>but I wanted to ask about the hang/panic you >mentioned in the cover letter when efi_scratch gets clobbered. Can you >describe the same (for e.g. how to reproduce this).
When efi_switch_mm() gets called concurrently from two different CPUs --via arch_efi_call_virt_setup()-- due to lack of serialisation in uv_bios_call(), efi_scratch.prev_mm is overwritten and that's how all hell breaks loose, and that's when you see either a hang (the more frequent failure mode) or a panic.
In order to reproduce the problem you'd need, for example, a kernel module that makes use of uv_bios_call(), in which case a test case would be a loop with:
- 2 concurrent tasks both invoking uv_bios_call()
or - 2 concurrent tasks - one invoking uv_bios_call() - one, for example, accessing an EFI vars via efivars
>Nitpicks below: > > >On 01/09/2019 04:15 PM, Hedi Berriche wrote: >>Calls into UV firmware must be protected against concurrency, use the >>now visible efi_runtime_sem lock to serialise them. >> >>Signed-off-by: Hedi Berriche <hedi.berriche@hpe.com> >>Reviewed-by: Russ Anderson <rja@hpe.com> >>Reviewed-by: Mike Travis <mike.travis@hpe.com> >>Reviewed-by: Dimitri Sivanich <sivanich@hpe.com> >>Reviewed-by: Steve Wahl <steve.wahl@hpe.com> >>--- >> arch/x86/include/asm/uv/bios.h | 3 ++- >> arch/x86/platform/uv/bios_uv.c | 25 ++++++++++++++++++++++--- >> 2 files changed, 24 insertions(+), 4 deletions(-) >> >>diff --git a/arch/x86/include/asm/uv/bios.h b/arch/x86/include/asm/uv/bios.h >>index 4eee646544b2..33e94aa0b1ff 100644 >>--- a/arch/x86/include/asm/uv/bios.h >>+++ b/arch/x86/include/asm/uv/bios.h >>@@ -48,7 +48,8 @@ enum { >> BIOS_STATUS_SUCCESS = 0, >> BIOS_STATUS_UNIMPLEMENTED = -ENOSYS, >> BIOS_STATUS_EINVAL = -EINVAL, >>- BIOS_STATUS_UNAVAIL = -EBUSY >>+ BIOS_STATUS_UNAVAIL = -EBUSY, >>+ BIOS_STATUS_ABORT = -EINTR >> }; >> /* Address map parameters */ >>diff --git a/arch/x86/platform/uv/bios_uv.c b/arch/x86/platform/uv/bios_uv.c >>index cd05af157763..92f960798e20 100644 >>--- a/arch/x86/platform/uv/bios_uv.c >>+++ b/arch/x86/platform/uv/bios_uv.c >>@@ -29,7 +29,8 @@ >> struct uv_systab *uv_systab; >>-s64 uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, u64 a4, u64 a5) >>+s64 __uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, >>+ u64 a4, u64 a5) > >Can we make this static?
Will do.
>> { >> struct uv_systab *tab = uv_systab; >> s64 ret; >>@@ -44,13 +45,26 @@ s64 uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, u64 a4, u64 a5) >> * If EFI_OLD_MEMMAP is set, we need to fall back to using our old EFI >> * callback method, which uses efi_call() directly, with the kernel page tables: >> */ >>- if (unlikely(test_bit(EFI_OLD_MEMMAP, &efi.flags))) >>+ if (unlikely(efi_enabled(EFI_OLD_MEMMAP))) >> ret = efi_call((void *)__va(tab->function), (u64)which, a1, a2, a3, a4, a5); >> else >> ret = efi_call_virt_pointer(tab, function, (u64)which, a1, a2, a3, a4, a5); >> return ret; >> } >>+ >>+s64 uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, u64 a4, u64 a5) >>+{ >>+ s64 ret; >>+ >>+ if (down_interruptible(&efi_runtime_sem)) >>+ return BIOS_STATUS_ABORT; >>+ >>+ ret = __uv_bios_call(which, a1, a2, a3, a4, a5); >>+ up(&efi_runtime_sem); >>+ >>+ return ret; >>+} >> EXPORT_SYMBOL_GPL(uv_bios_call); >> s64 uv_bios_call_irqsave(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, >>@@ -59,10 +73,15 @@ s64 uv_bios_call_irqsave(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, >> unsigned long bios_flags; >> s64 ret; >>+ if (down_interruptible(&efi_runtime_sem)) >>+ return BIOS_STATUS_ABORT; >>+ >> local_irq_save(bios_flags); >>- ret = uv_bios_call(which, a1, a2, a3, a4, a5); >>+ ret = __uv_bios_call(which, a1, a2, a3, a4, a5); >> local_irq_restore(bios_flags); >>+ up(&efi_runtime_sem); >>+ >> return ret; >> } > >Thanks, >Bhupesh
Cheers, Hedi. -- Be careful of reading health books, you might die of a misprint. -- Mark Twain
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