On Wed, Feb 16, 2022 at 04:39:02PM +1000, Nicholas Piggin wrote: > The behaviour of the Address Translation Mode on Interrupt resource is > not consistently supported by all CPU versions or all KVM versions: > KVM-HV does not support mode 2, and does not support mode 3 on POWER7 or > early POWER9 processesors. KVM PR only supports mode 0. TCG supports all > modes (0, 2, 3). This leads to inconsistencies in guest behaviour and > could cause problems migrating guests. > > This was not noticable for Linux guests for a long time because the > kernel only uses modes 0 and 3, and it used to consider AIL-3 to be > advisory in that it would always keep the AIL-0 vectors around. Recent > Linux guests depend on the AIL mode working as specified in order to > support the SCV facility interrupt. If AIL-3 can not be provided, then > Linux must be given an error so it can disable the SCV facility, rather > than silently failing. > > Add the ail-mode-3 capability to specify that AIL-3 is supported. AIL-0 > is implied as the baseline, and AIL-2 is no longer supported by spapr. > AIL-2 is not known to be used by any software, but support in TCG could > be restored with an ail-mode-2 capability quite easily if a regression > is reported. > > Modify the H_SET_MODE Address Translation Mode on Interrupt resource > handler to check capabilities and correctly return error if not > supported. > > A heuristic is added for KVM to determine AIL-3 support before the > introduction of a new KVM CAP, because blanket disabling AIL-3 has too > much performance cost. > > Signed-off-by: Nicholas Piggin <npig...@gmail.com>
Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
[snip]
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index dc93b99189..1338c41f8f 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2563,6 +2563,35 @@ int kvmppc_has_cap_rpt_invalidate(void)
> return cap_rpt_invalidate;
> }
>
> +bool kvmppc_supports_ail_3(void)
> +{
> + PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
> +
> + /*
> + * KVM PR only supports AIL-0
> + */
> + if (kvmppc_is_pr(kvm_state)) {
> + return 0;
> + }
> +
> + /*
> + * KVM HV hosts support AIL-3 on POWER8 and above, except for radix
> + * mode on some early POWER9s.
> + */
> + if (!(pcc->insns_flags2 & PPC2_ISA207S)) {
> + return 0;
> + }
> +
> + /* These tests match the CPU_FTR_P9_RADIX_PREFETCH_BUG flag in Linux */
> + if (((pcc->pvr & 0xffffff00) == CPU_POWERPC_POWER9_DD1) ||
> + ((pcc->pvr & 0xffffff00) == CPU_POWERPC_POWER9_DD20) ||
> + ((pcc->pvr & 0xffffff00) == CPU_POWERPC_POWER9_DD21)) {
> + return 0;
> + }
Deducing what KVM supports rather than getting it to tell us
explicitly with a cap is usually frowned upon. However, given the
earlier discussion, I'm satisfied that this is the least bad available
option, at least for now.
> +
> + return 1;
> +}
> +
> PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void)
> {
> uint32_t host_pvr = mfpvr();
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index ee9325bf9a..7bba26d1da 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -73,6 +73,7 @@ int kvmppc_set_cap_nested_kvm_hv(int enable);
> int kvmppc_get_cap_large_decr(void);
> int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable);
> int kvmppc_has_cap_rpt_invalidate(void);
> +bool kvmppc_supports_ail_3(void);
> int kvmppc_enable_hwrng(void);
> int kvmppc_put_books_sregs(PowerPCCPU *cpu);
> PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
> @@ -393,6 +394,11 @@ static inline int kvmppc_has_cap_rpt_invalidate(void)
> return false;
> }
>
> +static inline bool kvmppc_supports_ail_3(void)
> +{
> + return false;
> +}
> +
> static inline int kvmppc_enable_hwrng(void)
> {
> return -1;
--
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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