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SubjectRe: [PATCH 3/3] x86/platform/UV: use efi_runtime_sem to serialise BIOS calls
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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