On Fri, 11 Sep 2020 01:16:07 -0300
Fabiano Rosas <farosas@xxxxxxxxxxxxx> wrote:
> The current nested KVM code does not support HPT guests. This is
> informed/enforced in some ways:
>
> - Hosts < P9 will not be able to enable the nested HV feature;
>
> - The nested hypervisor MMU capabilities will not contain
> KVM_CAP_PPC_MMU_HASH_V3;
>
> - QEMU reflects the MMU capabilities in the
> 'ibm,arch-vec-5-platform-support' device-tree property;
>
> - The nested guest, at 'prom_parse_mmu_model' ignores the
> 'disable_radix' kernel command line option if HPT is not supported;
>
> - The KVM_PPC_CONFIGURE_V3_MMU ioctl will fail if trying to use HPT.
>
> There is, however, still a way to start a HPT guest by using
> max-compat-cpu=power8 at the QEMU machine options. This leads to the
> guest being set to use hash after QEMU calls the KVM_PPC_ALLOCATE_HTAB
> ioctl.
>
> With the guest set to hash, the nested hypervisor goes through the
> entry path that has no knowledge of nesting (kvmppc_run_vcpu) and
> crashes when it tries to execute an hypervisor-privileged (mtspr
> HDEC) instruction at __kvmppc_vcore_entry:
>
> root@L1:~ $ qemu-system-ppc64 -machine pseries,max-cpu-compat=power8 ...
>
> <snip>
> [ 538.543303] CPU: 83 PID: 25185 Comm: CPU 0/KVM Not tainted 5.9.0-rc4 #1
> [ 538.543355] NIP: c00800000753f388 LR: c00800000753f368 CTR: c0000000001e5ec0
> [ 538.543417] REGS: c0000013e91e33b0 TRAP: 0700 Not tainted (5.9.0-rc4)
> [ 538.543470] MSR: 8000000002843033 <SF,VEC,VSX,FP,ME,IR,DR,RI,LE> CR: 22422882 XER: 20040000
> [ 538.543546] CFAR: c00800000753f4b0 IRQMASK: 3
> GPR00: c0080000075397a0 c0000013e91e3640 c00800000755e600 0000000080000000
> GPR04: 0000000000000000 c0000013eab19800 c000001394de0000 00000043a054db72
> GPR08: 00000000003b1652 0000000000000000 0000000000000000 c0080000075502e0
> GPR12: c0000000001e5ec0 c0000007ffa74200 c0000013eab19800 0000000000000008
> GPR16: 0000000000000000 c00000139676c6c0 c000000001d23948 c0000013e91e38b8
> GPR20: 0000000000000053 0000000000000000 0000000000000001 0000000000000000
> GPR24: 0000000000000001 0000000000000001 0000000000000000 0000000000000001
> GPR28: 0000000000000001 0000000000000053 c0000013eab19800 0000000000000001
> [ 538.544067] NIP [c00800000753f388] __kvmppc_vcore_entry+0x90/0x104 [kvm_hv]
> [ 538.544121] LR [c00800000753f368] __kvmppc_vcore_entry+0x70/0x104 [kvm_hv]
> [ 538.544173] Call Trace:
> [ 538.544196] [c0000013e91e3640] [c0000013e91e3680] 0xc0000013e91e3680 (unreliable)
> [ 538.544260] [c0000013e91e3820] [c0080000075397a0] kvmppc_run_core+0xbc8/0x19d0 [kvm_hv]
> [ 538.544325] [c0000013e91e39e0] [c00800000753d99c] kvmppc_vcpu_run_hv+0x404/0xc00 [kvm_hv]
> [ 538.544394] [c0000013e91e3ad0] [c0080000072da4fc] kvmppc_vcpu_run+0x34/0x48 [kvm]
> [ 538.544472] [c0000013e91e3af0] [c0080000072d61b8] kvm_arch_vcpu_ioctl_run+0x310/0x420 [kvm]
> [ 538.544539] [c0000013e91e3b80] [c0080000072c7450] kvm_vcpu_ioctl+0x298/0x778 [kvm]
> [ 538.544605] [c0000013e91e3ce0] [c0000000004b8c2c] sys_ioctl+0x1dc/0xc90
> [ 538.544662] [c0000013e91e3dc0] [c00000000002f9a4] system_call_exception+0xe4/0x1c0
> [ 538.544726] [c0000013e91e3e20] [c00000000000d140] system_call_common+0xf0/0x27c
> [ 538.544787] Instruction dump:
> [ 538.544821] f86d1098 60000000 60000000 48000099 e8ad0fe8 e8c500a0 e9264140 75290002
> [ 538.544886] 7d1602a6 7cec42a6 40820008 7d0807b4 <7d164ba6> 7d083a14 f90d10a0 480104fd
> [ 538.544953] ---[ end trace 74423e2b948c2e0c ]---
>
> This patch makes the KVM_PPC_ALLOCATE_HTAB ioctl fail when running in
> the nested hypervisor, causing QEMU to abort.
>
> Reported-by: Satheesh Rajendran <sathnaga@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx>
> ---
LGTM
Reviewed-by: Greg Kurz <groug@xxxxxxxx>
> arch/powerpc/kvm/book3s_hv.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 4ba06a2a306c..764b6239ef72 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -5250,6 +5250,12 @@ static long kvm_arch_vm_ioctl_hv(struct file *filp,
> case KVM_PPC_ALLOCATE_HTAB: {
> u32 htab_order;
>
> + /* If we're a nested hypervisor, we currently only support radix */
> + if (kvmhv_on_pseries()) {
> + r = -EOPNOTSUPP;
> + break;
> + }
> +
> r = -EFAULT;
> if (get_user(htab_order, (u32 __user *)argp))
> break;
