Re: [PATCH v3] target: ppc: Use MSR_HVB bit to get the target endianness for memory dump

[Narayana Murty N <nnmlinux@linux.vnet.ibm.com>]

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On 5/23/23 15:52, Cédric Le Goater wrote:
> On 5/22/23 18:02, Narayana Murty N wrote:
>> Currently on PPC64 qemu always dumps the guest memory in
>> Big Endian (BE) format even though the guest running in Little Endian
>
>
>
> The patch is surely correct. I have problems understanding the config
> you are testing. PPC Book3s has multiple hypervisor implementations :
>
> 1. pHyp (AKA PowerVM)
> 2. OPAL/PowerNV (AKA Power KVM-HV)
> 3. OPAL/PowerNV/pSeries (AKA Power KVMHV-on-pSeries)
> 4. pHyp/pSeries (very recent implementation, I don't know how it is
>    referred to in the kernel)
>
> I am leaving the KVM-PR implementation out of the discussions for
> simplicity.
>
> QEMU also supports emulation of 2. and 3. in two different machines
> PowerNV and pseries, although running pseries guests under a PowerNV
> machine is slow, so is running pseries guests under pseries.
>
> Could you please describe your environment ?
>
> Thanks,
>
> C.
>
>
It had been tested target machine OPAL/PowerNV with big endian host os.
and also target OPAL/PowerNV/pSeries little endian host setup with qemu.

>
>> (LE) mode. So crash tool fails to load the dump as illustrated below:
>>
>> Log :
>> $ virsh dump DOMAIN --memory-only dump.file
>>
>> Domain 'DOMAIN' dumped to dump.file
>>
>> $ crash vmlinux dump.file
>>
>> <snip>
>> crash 8.0.2-1.el9
>>
>> WARNING: endian mismatch:
>>            crash utility: little-endian
>>            dump.file: big-endian
>>
>> WARNING: machine type mismatch:
>>            crash utility: PPC64
>>            dump.file: (unknown)
>>
>> crash: dump.file: not a supported file format
>> <snip>
>>
>> This happens because cpu_get_dump_info() passes cpu->env->has_hv_mode
>> to function ppc_interrupts_little_endian(), the cpu->env->has_hv_mode
>> always set for powerNV even though the guest is not running in hv mode.
>> The hv mode should be taken from msr_mask MSR_HVB bit
>> (cpu->env.msr_mask & MSR_HVB). This patch fixes the issue by passing
>> MSR_HVB value to ppc_interrupts_little_endian() in order to determine
>> the guest endianness.
>>
>> The crash tool also expects guest kernel endianness should match the
>> endianness of the dump.
>>
>> The patch was tested on POWER9 box booted with Linux as host in
>> following cases:
>>
>> Host-Endianess Qemu-Target-Machine Qemu-Guest-Endianess 
>> Qemu-Generated-Guest
>> Memory-Dump-Format
>> BE             powernv             LE KVM guest LE
>> BE             powernv             BE KVM guest BE
>> LE             powernv             LE KVM guest LE
>> LE             powernv             BE KVM guest BE
>> LE             pseries KVM         LE KVM guest LE
>> LE             pseries TCG         LE guest LE
>>
>> Signed-off-by: Narayana Murty N <nnmlinux@linux.ibm.com>
>> ---
>> Changes since V2:
>> commit message modified as per feedbak from Nicholas Piggin.
>> Changes since V1:
>> https://lore.kernel.org/qemu-devel/20230420145055.10196-1-nnmlinux@linux.ibm.com/ 
>>
>> The approach to solve the issue was changed based on feedback from
>> Fabiano Rosas on patch V1.
>> ---
>>   target/ppc/arch_dump.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/target/ppc/arch_dump.c b/target/ppc/arch_dump.c
>> index f58e6359d5..a8315659d9 100644
>> --- a/target/ppc/arch_dump.c
>> +++ b/target/ppc/arch_dump.c
>> @@ -237,7 +237,7 @@ int cpu_get_dump_info(ArchDumpInfo *info,
>>       info->d_machine = PPC_ELF_MACHINE;
>>       info->d_class = ELFCLASS;
>>   -    if (ppc_interrupts_little_endian(cpu, cpu->env.has_hv_mode)) {
>> +    if (ppc_interrupts_little_endian(cpu, !!(cpu->env.msr_mask & 
>> MSR_HVB))) {
>>           info->d_endian = ELFDATA2LSB;
>>       } else {
>>           info->d_endian = ELFDATA2MSB;
>

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