Re: [Qemu-devel] [PATCH 3/3] ppc/kvm: check some capabilities with kvm_vm_check_extension()

[Thomas Huth]

On 14.09.2017 21:25, Greg Kurz wrote:
> The following capabilities are VM specific:
> - KVM_CAP_PPC_SMT_POSSIBLE
> - KVM_CAP_PPC_HTAB_FD

BTW, looks like kvmppc_has_cap_htab_fd() is dead code ... should we
either remove it or check it somewhere?

> - KVM_CAP_PPC_ALLOC_HTAB
> 
> If both KVM HV and KVM PR are present, checking them always return
> the HV value, even if we explicitely requested to use PR.
> 
> This has no visible effect for KVM_CAP_PPC_ALLOC_HTAB, because we also
> try the KVM_PPC_ALLOCATE_HTAB ioctl which is only suppored by HV. As
> a consequence, the spapr code doesn't even check KVM_CAP_PPC_HTAB_FD.
>
> However, this will cause kvmppc_hint_smt_possible(), introduced by
> commit fa98fbfcdfcb9, to report several VSMT modes (eg, Available
> VSMT modes: 8 4 2 1) whereas PR only support mode 1.
> 
> This patch fixes all three anyway to use kvm_vm_check_extension(). It
> is okay since the VM is already created at the time kvm_arch_init() or
> kvmppc_reset_htab() is called.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  target/ppc/kvm.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 1deaf106d2b9..208c70e81426 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -131,7 +131,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      cap_interrupt_level = kvm_check_extension(s, KVM_CAP_PPC_IRQ_LEVEL);
>      cap_segstate = kvm_check_extension(s, KVM_CAP_PPC_SEGSTATE);
>      cap_booke_sregs = kvm_check_extension(s, KVM_CAP_PPC_BOOKE_SREGS);
> -    cap_ppc_smt_possible = kvm_check_extension(s, KVM_CAP_PPC_SMT_POSSIBLE);
> +    cap_ppc_smt_possible = kvm_vm_check_extension(s, 
> KVM_CAP_PPC_SMT_POSSIBLE);
>      cap_ppc_rma = kvm_check_extension(s, KVM_CAP_PPC_RMA);
>      cap_spapr_tce = kvm_check_extension(s, KVM_CAP_SPAPR_TCE);
>      cap_spapr_tce_64 = kvm_check_extension(s, KVM_CAP_SPAPR_TCE_64);
> @@ -143,7 +143,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      cap_ppc_watchdog = kvm_check_extension(s, KVM_CAP_PPC_BOOKE_WATCHDOG);
>      /* Note: we don't set cap_papr here, because this capability is
>       * only activated after this by kvmppc_set_papr() */
> -    cap_htab_fd = kvm_check_extension(s, KVM_CAP_PPC_HTAB_FD);
> +    cap_htab_fd = kvm_vm_check_extension(s, KVM_CAP_PPC_HTAB_FD);
>      cap_fixup_hcalls = kvm_check_extension(s, KVM_CAP_PPC_FIXUP_HCALL);
>      cap_ppc_smt = kvm_vm_check_extension(s, KVM_CAP_PPC_SMT);
>      cap_htm = kvm_vm_check_extension(s, KVM_CAP_PPC_HTM);
> @@ -2353,7 +2353,7 @@ int kvmppc_reset_htab(int shift_hint)
>          /* Full emulation, tell caller to allocate htab itself */
>          return 0;
>      }
> -    if (kvm_check_extension(kvm_state, KVM_CAP_PPC_ALLOC_HTAB)) {
> +    if (kvm_vm_check_extension(kvm_state, KVM_CAP_PPC_ALLOC_HTAB)) {
>          int ret;
>          ret = kvm_vm_ioctl(kvm_state, KVM_PPC_ALLOCATE_HTAB, &shift);
>          if (ret == -ENOTTY) {

Looking at the comment in the code after the "if (ret == -ENOTTY)" line,
it sounds like there is a bug in the kernel and the
KVM_CAP_PPC_ALLOC_HTAB should depend on the hv_enabled variable, too?
Anyway, that's another topic, your patch is fine!

Reviewed-by: Thomas Huth <address@hidden>