Re: [PATCH v3 4/8] acpi/ghes: Extend acpi_ghes_memory_errors() to support multiple CPERs

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 11 Nov 2025 14:40:42 +1000
Gavin Shan <gshan@redhat.com> wrote:

> Hi Igor,
> 
> On 11/11/25 12:38 AM, Igor Mammedov wrote:
> > On Wed,  5 Nov 2025 21:44:49 +1000
> > Gavin Shan <gshan@redhat.com> wrote:
> >   
> >> In the situation where host and guest has 64KiB and 4KiB page sizes,
> >> one problematic host page affects 16 guest pages. we need to send 16
> >> consective errors in this specific case.  
> > 
> > I still don't like it, since it won't fix anything in case of more than
> > 1 broken host pages. (in v2 discussion quickly went hugepages route
> > and futility of recovering from them).
> > 
> > If having per vCPU source is not desirable,
> > can we stall all other vcpus that touch poisoned pages until
> > error is acked by guest and then let another VCPU to queue its own error?
> >   
> 
> We're trying to avoid the guest from suddenly disappearing due to the QEMU
> crash, instead of recovering from the memory errors. To keep the guest
> accessible, system administrators still get a chance to collect important
> information from the guest.
> 
> The idea of stalling the vCPU which is accessing any poisoned pages and
> retry on delivering the error was proposed in v1, but was rejected.
> 
> https://lists.nongnu.org/archive/html/qemu-arm/2025-02/msg01071.html

that depends on what outcome we do wish for.
Described deadlock might be even desired vs QEMU abort() as it lets
guest admin to collect VM crash dump.

But honestly I'd go with per/vCPU approach if it's possible,
as that still get guest side chance to recover.


> As the intention of this series is just to improve the memory error
> reporting, to avoid QEMU crash if possible, it sounds reasonable to send
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
that,
this series doesn't do that as it would still crash QEMU if another
vCPU faults on another faulty host page (i.e. not the one we've generated CPERs)

You also mentioned in previous review that with per vCPU error source
variant that QEMU would abort elsewhere (is it fixable?).

> 16x consecutive CPERs in one shot for this specific case (4KB guest on
> 64KB host).

I don't object to generating 16x CPERs per fault as that obviously
should reduce # of guest exits. 



Given it's rather late in release cycle,
we probably can handle 1 page case 1st as in this series,
with followup series to switch to per/vCPU variant once new merge
window opens (assuming I can coax a promise from you to follow up on that).

>As to hugetlb cases, it's different story. If the hugetlb
> folio (page) size is small enough (like 64KB), we can leverage current
> design to send consecutive CPERs. I don't think there are too much we
> can do if hugetlb folio size is large enough (from 2MB to 16GB).
> 
> >   
> >> Extend acpi_ghes_memory_errors() to support multiple CPERs after the
> >> hunk of code to generate the GHES error status is pulled out from
> >> ghes_gen_err_data_uncorrectable_recoverable(). The status field of
> >> generic error status block is also updated accordingly if multiple
> >> error data entries are contained in the generic error status block.  
> > 
> > I don't mind much translating 64K page error into several 4K CPER
> > records, so this part is fine. But it's hardly a solution to the generic
> > problem.
> >   
> 
> Note that I don't expect a memory error storm from the hardware level.
> In that case, it's a good sign indicating the memory DIMM has been totally
> broken and needs a replacement :-)
> 
> >>
> >> Signed-off-by: Gavin Shan <gshan@redhat.com>
> >> ---
> >>   hw/acpi/ghes-stub.c    |  2 +-
> >>   hw/acpi/ghes.c         | 60 +++++++++++++++++++++++-------------------
> >>   include/hw/acpi/ghes.h |  2 +-
> >>   target/arm/kvm.c       |  4 ++-
> >>   4 files changed, 38 insertions(+), 30 deletions(-)
> >>  
> > ...  
> >> @@ -577,10 +568,25 @@ int acpi_ghes_memory_errors(AcpiGhesState *ags, uint16_t source_id,
> >>       assert((data_length + ACPI_GHES_GESB_SIZE) <=
> >>               ACPI_GHES_MAX_RAW_DATA_LENGTH);
> >>   
> >> -    ghes_gen_err_data_uncorrectable_recoverable(block, guid, data_length);
> >> +    /* Build the new generic error status block header */
> >> +    block_status = (1 << ACPI_GEBS_UNCORRECTABLE) |
> >> +                   (num_of_addresses << ACPI_GEBS_ERROR_DATA_ENTRIES);  
> >                         ^^^^^^^^^^^^^^
> > maybe assert in case it won't fit into bit field
> >   
> 
> Yep, Same thing was suggested by Philippe.
> 
> >> +    if (num_of_addresses > 1) {
> >> +        block_status |= ACPI_GEBS_MULTIPLE_UNCORRECTABLE;
> >> +    }
> >> +
> >> +    acpi_ghes_generic_error_status(block, block_status, 0, 0,
> >> +                                   data_length, ACPI_CPER_SEV_RECOVERABLE);
> >>   
> >> -    /* Build the memory section CPER for above new generic error data entry */
> >> -    acpi_ghes_build_append_mem_cper(block, physical_address);
> >> +    for (i = 0; i < num_of_addresses; i++) {
> >> +        /* Build generic error data entries */
> >> +        acpi_ghes_generic_error_data(block, guid,
> >> +                                     ACPI_CPER_SEV_RECOVERABLE, 0, 0,
> >> +                                     ACPI_GHES_MEM_CPER_LENGTH, fru_id, 0);
> >> +
> >> +        /* Memory section CPER on top of the generic error data entry */
> >> +        acpi_ghes_build_append_mem_cper(block, addresses[i]);
> >> +    }
> >>   
> >>       /* Report the error */
> >>       ghes_record_cper_errors(ags, block->data, block->len, source_id, &errp);
> >> diff --git a/include/hw/acpi/ghes.h b/include/hw/acpi/ghes.h
> >> index df2ecbf6e4..f73908985d 100644
> >> --- a/include/hw/acpi/ghes.h
> >> +++ b/include/hw/acpi/ghes.h
> >> @@ -99,7 +99,7 @@ void acpi_build_hest(AcpiGhesState *ags, GArray *table_data,
> >>   void acpi_ghes_add_fw_cfg(AcpiGhesState *vms, FWCfgState *s,
> >>                             GArray *hardware_errors);
> >>   int acpi_ghes_memory_errors(AcpiGhesState *ags, uint16_t source_id,
> >> -                            uint64_t error_physical_addr);
> >> +                            uint64_t *addresses, uint32_t num_of_addresses);
> >>   void ghes_record_cper_errors(AcpiGhesState *ags, const void *cper, size_t len,
> >>                                uint16_t source_id, Error **errp);
> >>   
> >> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> >> index 0d57081e69..459ca4a9b0 100644
> >> --- a/target/arm/kvm.c
> >> +++ b/target/arm/kvm.c
> >> @@ -2434,6 +2434,7 @@ void kvm_arch_on_sigbus_vcpu(CPUState *c, int code, void *addr)
> >>       ram_addr_t ram_addr;
> >>       hwaddr paddr;
> >>       AcpiGhesState *ags;
> >> +    uint64_t addresses[16];
> >>   
> >>       assert(code == BUS_MCEERR_AR || code == BUS_MCEERR_AO);
> >>   
> >> @@ -2454,10 +2455,11 @@ void kvm_arch_on_sigbus_vcpu(CPUState *c, int code, void *addr)
> >>                * later from the main thread, so doing the injection of
> >>                * the error would be more complicated.
> >>                */
> >> +            addresses[0] = paddr;
> >>               if (code == BUS_MCEERR_AR) {
> >>                   kvm_cpu_synchronize_state(c);
> >>                   if (!acpi_ghes_memory_errors(ags, ACPI_HEST_SRC_ID_SYNC,
> >> -                                             paddr)) {
> >> +                                             addresses, 1)) {
> >>                       kvm_inject_arm_sea(c);
> >>                   } else {
> >>                       error_report("failed to record the error");  
> >   
> 
> Thanks,
> Gavin
>