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

[Gavin Shan <gshan@redhat.com>]

Hi Jonathan,

On 11/18/25 8:47 PM, 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).
> 
> Will keep everyone informed of how we get on with resolving that.
> 

Thanks, Jonathan. If the broader address mask in CPER can be used to isolate
the specified memory range instead of a page, QEMU needn't the improvement
done in this series. Please copy me if the linux patches are going to be
sent for review if possible, I will try to review.

I will pull those patches improving error handling and post them separately
so that they can be merged. Those patches aren't really relevant to error handling.

Thanks,
Gavin