Re: [PATCH 0/4] target/arm: Improvement on memory error handling

[Mauro Carvalho Chehab <mchehab+huawei@kernel.org>]

Em Fri, 14 Feb 2025 14:16:31 +1000
Gavin Shan <gshan@redhat.com> escreveu:

> Currently, there is only one CPER buffer (entry), meaning only one
> memory error can be reported. In extreme case, multiple memory errors
> can be raised on different vCPUs. For example, a singile memory error
> on a 64KB page of the host can results in 16 memory errors to 4KB
> pages of the guest. 

There is already a patchset allowing to have multiple CPER entries
floating around since last year:

	https://lore.kernel.org/qemu-devel/cover.1738345063.git.mchehab+huawei@kernel.org/

I guess it is almost ready for being merged, needing just some
nitpick changes to satisfy ACPI maintainers. Such changeset already
adds a second CPER entry for GED, and allows to easily add more as
needed. 

> In extreme case, multiple memory errors
> can be raised on different vCPUs. For example, a singile memory error
> on a 64KB page of the host can results in 16 memory errors to 4KB
> pages of the guest. 

> Unfortunately, the virtual machine is simply aborted
> by multiple concurrent memory errors, as the following call trace shows.
> A SEA exception is injected to the guest so that the CPER buffer can
> be claimed if the error is successfully pushed by acpi_ghes_memory_errors(),
> Otherwise, abort() is triggered to crash the virtual machine.
> 
>   kvm_vcpu_thread_fn
>     kvm_cpu_exec
>       kvm_arch_on_sigbus_vcpu
>         kvm_cpu_synchronize_state
>         acpi_ghes_memory_errors         (a)
>         kvm_inject_arm_sea | abort
> 
> It's arguably to crash the virtual machine in this case. The better
> behaviour would be to retry on pushing the memory errors, to keep the
> virtual machine alive so that the administrator has chance to chime
> in, for example to dump the important data with luck. This series
> adds one more parameter to acpi_ghes_memory_errors() so that it will
> be tried to push the memory error until it succeeds.

Having a retry buffer might be interesting for some types of errors,
like error-injected and corrected errors. Yet, it doesn't sound right 
to buffer uncorrected errors that would affect the virtual machine.

> 
> Gavin Shan (4):
>   acpi/ghes: Make ghes_record_cper_errors() static
>   acpi/ghes: Use error_report() in ghes_record_cper_errors()
>   acpi/ghes: Allow retry to write CPER errors
>   target/arm: Retry pushing CPER error if necessary
> 
>  hw/acpi/ghes-stub.c    |  3 ++-
>  hw/acpi/ghes.c         | 45 +++++++++++++++++++++---------------------
>  include/hw/acpi/ghes.h |  5 ++---
>  target/arm/kvm.c       | 31 +++++++++++++++++++++++------
>  4 files changed, 51 insertions(+), 33 deletions(-)
> 



Thanks,
Mauro