[PATCH] target/ppc/mmu_common: Fix SRR1/MSR error code on Book-E

[Vitaly Cheptsov]

Hello,

PowerPC e500mc defines MSR bit 35 differently from most other PowerPC variants. 
In particular, for e500mc this is GS (Guest Supervisor) bit[1], while for 
others it is NOEXEC GUARD bit[2].
QEMU ignores this architectural difference when handling the exceptions of 
attempting to run not executable code on e500mc, and mistakenly sets the GS 
bit[3][4].
Setting this bit eventually leads to crashes, because although QEMU does not 
support Guest Supervisor mode on e500mc, it still requires it to be disabled[5].

Best regards,
Vitaly

[1] https://www.nxp.com/docs/en/reference-manual/E500MCRM.pdf, 2.7.1 MSR
[2] https://openpowerfoundation.org/?resource_lib=power-isa-version-3-0, 6.5.5 
Instruction Storage Interrupt
[3] https://github.com/qemu/qemu/blob/v6.2.0/target/ppc/mmu_common.c#L1426
[4] https://github.com/qemu/qemu/blob/v6.2.0/target/ppc/excp_helper.c#L414-L416
[5] https://github.com/qemu/qemu/blob/v6.2.0/target/ppc/mmu_helper.c#L1078-L1080

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