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Re: [PATCH qemu] ppc/kvm: Skip writing DPDES back when in run time state
From: |
David Gibson |
Subject: |
Re: [PATCH qemu] ppc/kvm: Skip writing DPDES back when in run time state |
Date: |
Tue, 24 Sep 2019 23:18:36 +1000 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
On Mon, Sep 23, 2019 at 06:41:10PM +1000, Alexey Kardashevskiy wrote:
> 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 <address@hidden>
Applied to ppc-for-4.2, thanks.
> ---
> target/ppc/kvm.c | 5 +++++
> target/ppc/translate_init.inc.c | 9 ++++-----
> 2 files changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 8c5b1f25cc95..820724cc7d15 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -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
> }
>
> diff --git a/target/ppc/translate_init.inc.c b/target/ppc/translate_init.inc.c
> index 0fb11c7ac6da..ba726dec4d00 100644
> --- a/target/ppc/translate_init.inc.c
> +++ b/target/ppc/translate_init.inc.c
> @@ -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
> }
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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