mirrors/qemu
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

ppc/kvm: Skip writing DPDES back when in run time state

Browse Source 
On POWER8 systems the Directed Privileged Door-bell Exception State
register (DPDES) stores doorbell pending status, one bit per a thread
of a core, set by "msgsndp" instruction. The register is shared among
threads of the same core and KVM on POWER9 emulates it in a similar way
(POWER9 does not have DPDES).

DPDES is shared but QEMU assumes all SPRs are per thread so the only safe
way to write DPDES back to VCPU before running a guest is doing so
while all threads are pulled out of the guest so DPDES cannot change.
There is only one situation when this condition is met: incoming migration
when all threads are stopped. Otherwise any QEMU HMP/QMP command causing
kvm_arch_put_registers() (for example printing registers or dumping memory)
can clobber DPDES in a race with other vcpu threads.

This changes DPDES handling so it is not written to KVM at runtime.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20190923084110.34643-1-aik@ozlabs.ru>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Alexey Kardashevskiy 2019-09-23 18:41:10 +10:00 committed by David Gibson
parent 5c94dd3806
commit 972bd57689
2 changed files with 9 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
target/ppc/kvm.c
View File

@ -993,6 +993,10 @@ int kvm_arch_put_registers(CPUState *cs, int level)
}
kvm_set_one_reg(cs, KVM_REG_PPC_TB_OFFSET, &env->tb_env->tb_offset);
if (level > KVM_PUT_RUNTIME_STATE) {
kvm_put_one_spr(cs, KVM_REG_PPC_DPDES, SPR_DPDES);
}
#endif /* TARGET_PPC64 */
}
@ -1297,6 +1301,7 @@ int kvm_arch_get_registers(CPUState *cs)
}
kvm_get_one_reg(cs, KVM_REG_PPC_TB_OFFSET, &env->tb_env->tb_offset);
kvm_get_one_spr(cs, KVM_REG_PPC_DPDES, SPR_DPDES);
#endif
}

9
target/ppc/translate_init.inc.c
View File

@ -8200,11 +8200,10 @@ static void gen_spr_power8_dpdes(CPUPPCState *env)
{
#if !defined(CONFIG_USER_ONLY)
/* Directed Privileged Door-bell Exception State, used for IPI */
spr_register_kvm_hv(env, SPR_DPDES, "DPDES",
SPR_NOACCESS, SPR_NOACCESS,
&spr_read_generic, SPR_NOACCESS,
&spr_read_generic, &spr_write_generic,
KVM_REG_PPC_DPDES, 0x00000000);
spr_register(env, SPR_DPDES, "DPDES",
SPR_NOACCESS, SPR_NOACCESS,
&spr_read_generic, SPR_NOACCESS,
0x00000000);
#endif
}