[PATCH v4] target: ppc: Use MSR_HVB bit to get the target endianness for memory dump

[Narayana Murty N]

Currently on PPC64 qemu always dumps the guest memory in
Big Endian (BE) format even though the guest running in Little Endian
(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-Generated-Guest
                                                  Memory-Dump-Format
BE             powernv(OPAL/PowerNV)                   LE
BE             powernv(OPAL/PowerNV)                   BE
LE             powernv(OPAL/PowerNV)                   LE
LE             powernv(OPAL/PowerNV)                   BE
LE             pseries(OPAL/PowerNV/pSeries) KVMHV     LE
LE             pseries TCG                             LE

Fixes: 5609400a4228 ("target/ppc: Set the correct endianness for powernv memory
dumps")
Signed-off-by: Narayana Murty N <nnmlinux@linux.ibm.com>
---
Changes since V3:
commit message modified as per feedback from Greg Kurz, Cédric Le
Goater and Nicholas Piggin.
Changes since V2:
commit message modified as per feedback 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;
-- 
2.39.2