Re: [PATCH v4 0/8] target/arm/kvm: Improve memory error handling

[Gavin Shan <gshan@redhat.com>]

Hi Mauro,

On 11/18/25 8:54 PM, Mauro Carvalho Chehab wrote:
> On Tue, Nov 18, 2025 at 10:47:55AM +0000, Jonathan Cameron wrote:
>> On Thu, 13 Nov 2025 03:25:27 +1000
>> Gavin Shan <gshan@redhat.com> wrote:
>>
>>> In the combination of 64KiB host and 4KiB guest, a problematic host
>>> page affects 16x guest pages. Those 16x guest pages are most likely
>>> owned by separate threads and accessed by the threads in parallel.
>>> It means 16x memory errors can be raised at once. However, we're
>>> unable to handle this situation because the only error source has
>>> one read acknowledgement register in current design. QEMU has to
>>> crash in the following path due to the previously delivered error
>>> isn't acknowledged by the guest on attempt to deliver another error.
>>>
>>>    kvm_vcpu_thread_fn
>>>      kvm_cpu_exec
>>>        kvm_arch_on_sigbus_vcpu
>>>          kvm_cpu_synchronize_state
>>>          acpi_ghes_memory_errors
>>>          abort
>>>
>>> This series fixes the issue by sending 16x consective CPER errors
>>> which are contained in a single GHES error block.
>>>
>>> PATCH[1-4] Increases GHES raw data maximal length from 1KiB to 4KiB
>>> PATCH[5]   Supports multiple error records in a single error block
>>> PATCH[6-7] Improves the error handling in the error delivery path
>>> PATCH[8]   Sends 16x consective CPERs in a single block if needed
>>>
>>
>> Hi Gavin,
>>
>> Just a quick head's up to say we've had some internal discussions around the
>> kernel handling of broader address masks in CPER and think it is probably
>> broken. Rectifying that may at least simplify what is needed on the QEMU side
>> of things and maybe even handle much larger blocks (2M and larger).
> 
> Btw, I just added a logic at rasdaemon to catch SIGBUS errors:
> https://github.com/mchehab/rasdaemon/pull/199
> 
> But so far, I didn't find a proper way to check such code.
> 
> Jonathan/Gavin,
> 
> Do you know a good way for us to check how the mm SEA notification
> is handled with QEMU?
> 

Sorry that I'm not familiar with rasdaemon. Could you please provide more
contexts about your question?

Thanks,
Gavin