Re: [PATCH RESEND v2 3/3] target/arm/kvm: Support multiple memory CPERs injection

[Gavin Shan <gshan@redhat.com>]

Hi Jonathan and Igor,

On 11/4/25 10:21 PM, Jonathan Cameron wrote:
> On Mon, 3 Nov 2025 10:52:16 +0100
> Igor Mammedov <imammedo@redhat.com> wrote:
> 

[...]

>> My idea using per cpu source is just a speculation based on spec
>> on how workaround the problem,
>> I don't really know if guest OS will be able to handle it (aka,
>> need to be tested is it's viable). That also probably was a reason
>> in previous review, why should've waited for multiple sources
>> support be be merged first before this series.
> 
> Per vCPU should work fine but I do like the approach here of reporting
> all the related errors in one go as they represent the underlying nature
> of the error granularity tracking. If anyone ever poisons at the 1GiB level
> on the host they are on their own - so I think that it will only ever be
> the finest granularity supported (so worse case 64KiB).
> 

Well, I don't have strong opinions, but I intend to agree with Jonathan
to report all 16x errors at once. One reason is one as Jonathan mentioned.
Another reason is per vCPU error source is a bit heavy for the improvement.

So I'm going to improve (v2) series to address all received comments and
post a (v3) series.

I already had the prototype of error source per vcpu, which works fine for
64KB-host-4KB-guest. However, it doesn't work for huge pages. For example,
a problematic 512MB huge page can cause heavy memory error storm to QEMU
where we absolutely can't handle.

1. Start the VM with hugetlb pages

/home/gavin/sandbox/qemu.main/build/qemu-system-aarch64                                     \
-accel kvm -machine virt,gic-version=host,nvdimm=on,ras=on                                  \
-cpu host -smp maxcpus=8,cpus=8,sockets=2,clusters=2,cores=2,threads=1                      \
-m 4096M,slots=16,maxmem=128G                                                               \
-object memory-backend-file,id=mem0,prealloc=on,mem-path=/dev/hugepages-524288kB,size=4096M \
-numa node,nodeid=0,cpus=0-7,memdev=mem0                                                    \

2. Run 'victim -d' on guest

guest$ ./victim -d
physical address of (0xffff889d6000) = 0x11a7da000
Hit any key to trigger error:

3. Inject error from host

host$ errinjct 0x11a7da000

4. QEMU crashes with error message "Bus error (core dumped)", which is triggered
the following path.

sigbus_handler
   kvm_on_sigbus_vcpu           // have_sigbus_pending = 1
   sigbus_reraise

Thanks,
Gavin