Re: [PATCH v2] KVM: PPC: Book3S HV: Fix L2 guest reboot failure due to empty 'arch_compat'

From: Aneesh Kumar K . V
Date: Mon Feb 05 2024 - 08:39:44 EST

Amit Machhiwal <amachhiw@xxxxxxxxxxxxx> writes:

> Currently, rebooting a pseries nested qemu-kvm guest (L2) results in
> below error as L1 qemu sends PVR value 'arch_compat' == 0 via
> ppc_set_compat ioctl. This triggers a condition failure in
> kvmppc_set_arch_compat() resulting in an EINVAL.
>
> qemu-system-ppc64: Unable to set CPU compatibility mode in KVM: Invalid
> argument
>
> Also, a value of 0 for arch_compat generally refers the default
> compatibility of the host. But, arch_compat, being a Guest Wide Element
> in nested API v2, cannot be set to 0 in GSB as PowerVM (L0) expects a
> non-zero value. A value of 0 triggers a kernel trap during a reboot and
> consequently causes it to fail:
>
> [ 22.106360] reboot: Restarting system
> KVM: unknown exit, hardware reason ffffffffffffffea
> NIP 0000000000000100 LR 000000000000fe44 CTR 0000000000000000 XER 0000000020040092 CPU#0
> MSR 0000000000001000 HID0 0000000000000000 HF 6c000000 iidx 3 didx 3
> TB 00000000 00000000 DECR 0
> GPR00 0000000000000000 0000000000000000 c000000002a8c300 000000007fe00000
> GPR04 0000000000000000 0000000000000000 0000000000001002 8000000002803033
> GPR08 000000000a000000 0000000000000000 0000000000000004 000000002fff0000
> GPR12 0000000000000000 c000000002e10000 0000000105639200 0000000000000004
> GPR16 0000000000000000 000000010563a090 0000000000000000 0000000000000000
> GPR20 0000000105639e20 00000001056399c8 00007fffe54abab0 0000000105639288
> GPR24 0000000000000000 0000000000000001 0000000000000001 0000000000000000
> GPR28 0000000000000000 0000000000000000 c000000002b30840 0000000000000000
> CR 00000000 [ - - - - - - - - ] RES 000@ffffffffffffffff
> SRR0 0000000000000000 SRR1 0000000000000000 PVR 0000000000800200 VRSAVE 0000000000000000
> SPRG0 0000000000000000 SPRG1 0000000000000000 SPRG2 0000000000000000 SPRG3 0000000000000000
> SPRG4 0000000000000000 SPRG5 0000000000000000 SPRG6 0000000000000000 SPRG7 0000000000000000
> HSRR0 0000000000000000 HSRR1 0000000000000000
> CFAR 0000000000000000
> LPCR 0000000000020400
> PTCR 0000000000000000 DAR 0000000000000000 DSISR 0000000000000000
>
> kernel:trap=0xffffffea | pc=0x100 | msr=0x1000
>
> This patch updates kvmppc_set_arch_compat() to use the host PVR value if
> 'compat_pvr' == 0 indicating that qemu doesn't want to enforce any
> specific PVR compat mode.
>

Reviewed-by: Aneesh Kumar K.V (IBM) <aneesh.kumar@xxxxxxxxxx>

>
> Fixes: 19d31c5f1157 ("KVM: PPC: Add support for nestedv2 guests")
> Signed-off-by: Amit Machhiwal <amachhiw@xxxxxxxxxxxxx>
> ---
>
> Changes v1 -> v2:
> - Added descriptive error log in the patch description when
> `arch_compat == 0` passed in GSB
> - Added a helper function for PCR to capabilities mapping
> - Added relevant comments around the changes being made
>
> v1: https://lore.kernel.org/lkml/20240118095653.2588129-1-amachhiw@xxxxxxxxxxxxx/
>
> arch/powerpc/kvm/book3s_hv.c | 25 +++++++++++++++++++++++--
> arch/powerpc/kvm/book3s_hv_nestedv2.c | 23 +++++++++++++++++++++--
> 2 files changed, 44 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 52427fc2a33f..270ab9cf9a54 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -391,6 +391,23 @@ static void kvmppc_set_pvr_hv(struct kvm_vcpu *vcpu, u32 pvr)
> /* Dummy value used in computing PCR value below */
> #define PCR_ARCH_31 (PCR_ARCH_300 << 1)
>
> +static inline unsigned long map_pcr_to_cap(unsigned long pcr)
> +{
> + unsigned long cap = 0;
> +
> + switch (pcr) {
> + case PCR_ARCH_300:
> + cap = H_GUEST_CAP_POWER9;
> + break;
> + case PCR_ARCH_31:
> + cap = H_GUEST_CAP_POWER10;
> + default:
> + break;
> + }
> +
> + return cap;
> +}
> +
> static int kvmppc_set_arch_compat(struct kvm_vcpu *vcpu, u32 arch_compat)
> {
> unsigned long host_pcr_bit = 0, guest_pcr_bit = 0, cap = 0;
> @@ -424,11 +441,9 @@ static int kvmppc_set_arch_compat(struct kvm_vcpu *vcpu, u32 arch_compat)
> break;
> case PVR_ARCH_300:
> guest_pcr_bit = PCR_ARCH_300;
> - cap = H_GUEST_CAP_POWER9;
> break;
> case PVR_ARCH_31:
> guest_pcr_bit = PCR_ARCH_31;
> - cap = H_GUEST_CAP_POWER10;
> break;
> default:
> return -EINVAL;
> @@ -440,6 +455,12 @@ static int kvmppc_set_arch_compat(struct kvm_vcpu *vcpu, u32 arch_compat)
> return -EINVAL;
>
> if (kvmhv_on_pseries() && kvmhv_is_nestedv2()) {
> + /*
> + * 'arch_compat == 0' would mean the guest should default to
> + * L1's compatibility. In this case, the guest would pick
> + * host's PCR and evaluate the corresponding capabilities.
> + */
> + cap = map_pcr_to_cap(guest_pcr_bit);
> if (!(cap & nested_capabilities))
> return -EINVAL;
> }
> diff --git a/arch/powerpc/kvm/book3s_hv_nestedv2.c b/arch/powerpc/kvm/book3s_hv_nestedv2.c
> index 5378eb40b162..6042bdc70230 100644
> --- a/arch/powerpc/kvm/book3s_hv_nestedv2.c
> +++ b/arch/powerpc/kvm/book3s_hv_nestedv2.c
> @@ -138,6 +138,7 @@ static int gs_msg_ops_vcpu_fill_info(struct kvmppc_gs_buff *gsb,
> vector128 v;
> int rc, i;
> u16 iden;
> + u32 arch_compat = 0;
>
> vcpu = gsm->data;
>
> @@ -347,8 +348,26 @@ static int gs_msg_ops_vcpu_fill_info(struct kvmppc_gs_buff *gsb,
> break;
> }
> case KVMPPC_GSID_LOGICAL_PVR:
> - rc = kvmppc_gse_put_u32(gsb, iden,
> - vcpu->arch.vcore->arch_compat);
> + /*
> + * Though 'arch_compat == 0' would mean the default
> + * compatibility, arch_compat, being a Guest Wide
> + * Element, cannot be filled with a value of 0 in GSB
> + * as this would result into a kernel trap.
> + * Hence, when `arch_compat == 0`, arch_compat should
> + * default to L1's PVR.
> + *
> + * Rework this when PowerVM supports a value of 0
> + * for arch_compat for KVM API v2.
> + */
> + if (!vcpu->arch.vcore->arch_compat) {
> + if (cpu_has_feature(CPU_FTR_ARCH_31))
> + arch_compat = PVR_ARCH_31;
> + else if (cpu_has_feature(CPU_FTR_ARCH_300))
> + arch_compat = PVR_ARCH_300;
> + } else {
> + arch_compat = vcpu->arch.vcore->arch_compat;
> + }
> + rc = kvmppc_gse_put_u32(gsb, iden, arch_compat);
> break;
> }
>
>
> base-commit: 6764c317b6bb91bd806ef79adf6d9c0e428b191e
> --
> 2.43.0