Re: [PATCH] KVM: arm64: Handle kvm_arm_init failure correctly in finalize_pkvm

[Sudeep Holla]

On Tue, Jul 11, 2023 at 09:36:46AM +0100, Marc Zyngier wrote:
> On Tue, 04 Jul 2023 20:32:43 +0100,
> Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
> > 
> > Currently there is no synchronisation between finalize_pkvm() and
> > kvm_arm_init() initcalls. The finalize_pkvm() proceeds happily even if
> > kvm_arm_init() fails resulting in the following warning on all the CPUs
> > and eventually a HYP panic:
> > 
> >   | kvm [1]: IPA Size Limit: 48 bits
> >   | kvm [1]: Failed to init hyp memory protection
> >   | kvm [1]: error initializing Hyp mode: -22
> >   |
> >   | <snip>
> >   |
> >   | WARNING: CPU: 0 PID: 0 at arch/arm64/kvm/pkvm.c:226 _kvm_host_prot_finalize+0x30/0x50
> >   | Modules linked in:
> >   | CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.4.0 #237
> >   | Hardware name: FVP Base RevC (DT)
> >   | pstate: 634020c5 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
> >   | pc : _kvm_host_prot_finalize+0x30/0x50
> >   | lr : __flush_smp_call_function_queue+0xd8/0x230
> >   |
> >   | Call trace:
> >   |  _kvm_host_prot_finalize+0x3c/0x50
> >   |  on_each_cpu_cond_mask+0x3c/0x6c
> >   |  pkvm_drop_host_privileges+0x4c/0x78
> >   |  finalize_pkvm+0x3c/0x5c
> >   |  do_one_initcall+0xcc/0x240
> >   |  do_initcall_level+0x8c/0xac
> >   |  do_initcalls+0x54/0x94
> >   |  do_basic_setup+0x1c/0x28
> >   |  kernel_init_freeable+0x100/0x16c
> >   |  kernel_init+0x20/0x1a0
> >   |  ret_from_fork+0x10/0x20
> >   | Failed to finalize Hyp protection: -22
> >   |     dtb=fvp-base-revc.dtb
> >   | kvm [95]: nVHE hyp BUG at: arch/arm64/kvm/hyp/nvhe/mem_protect.c:540!
> >   | kvm [95]: nVHE call trace:
> >   | kvm [95]:  [<ffff800081052984>] __kvm_nvhe_hyp_panic+0xac/0xf8
> >   | kvm [95]:  [<ffff800081059644>] __kvm_nvhe_handle_host_mem_abort+0x1a0/0x2ac
> >   | kvm [95]:  [<ffff80008105511c>] __kvm_nvhe_handle_trap+0x4c/0x160
> >   | kvm [95]:  [<ffff8000810540fc>] __kvm_nvhe___skip_pauth_save+0x4/0x4
> >   | kvm [95]: ---[ end nVHE call trace ]---
> >   | kvm [95]: Hyp Offset: 0xfffe8db00ffa0000
> >   | Kernel panic - not syncing: HYP panic:
> >   | PS:a34023c9 PC:0000f250710b973c ESR:00000000f2000800
> >   | FAR:ffff000800cb00d0 HPFAR:000000000880cb00 PAR:0000000000000000
> >   | VCPU:0000000000000000
> >   | CPU: 3 PID: 95 Comm: kworker/u16:2 Tainted: G        W          6.4.0 #237
> >   | Hardware name: FVP Base RevC (DT)
> >   | Workqueue: rpciod rpc_async_schedule
> >   | Call trace:
> >   |  dump_backtrace+0xec/0x108
> >   |  show_stack+0x18/0x2c
> >   |  dump_stack_lvl+0x50/0x68
> >   |  dump_stack+0x18/0x24
> >   |  panic+0x138/0x33c
> >   |  nvhe_hyp_panic_handler+0x100/0x184
> >   |  new_slab+0x23c/0x54c
> >   |  ___slab_alloc+0x3e4/0x770
> >   |  kmem_cache_alloc_node+0x1f0/0x278
> >   |  __alloc_skb+0xdc/0x294
> >   |  tcp_stream_alloc_skb+0x2c/0xf0
> >   |  tcp_sendmsg_locked+0x3d0/0xda4
> >   |  tcp_sendmsg+0x38/0x5c
> >   |  inet_sendmsg+0x44/0x60
> >   |  sock_sendmsg+0x1c/0x34
> >   |  xprt_sock_sendmsg+0xdc/0x274
> >   |  xs_tcp_send_request+0x1ac/0x28c
> >   |  xprt_transmit+0xcc/0x300
> >   |  call_transmit+0x78/0x90
> >   |  __rpc_execute+0x114/0x3d8
> >   |  rpc_async_schedule+0x28/0x48
> >   |  process_one_work+0x1d8/0x314
> >   |  worker_thread+0x248/0x474
> >   |  kthread+0xfc/0x184
> >   |  ret_from_fork+0x10/0x20
> >   | SMP: stopping secondary CPUs
> >   | Kernel Offset: 0x57c5cb460000 from 0xffff800080000000
> >   | PHYS_OFFSET: 0x80000000
> >   | CPU features: 0x00000000,1035b7a3,ccfe773f
> >   | Memory Limit: none
> >   | ---[ end Kernel panic - not syncing: HYP panic:
> >   | PS:a34023c9 PC:0000f250710b973c ESR:00000000f2000800
> >   | FAR:ffff000800cb00d0 HPFAR:000000000880cb00 PAR:0000000000000000
> >   | VCPU:0000000000000000 ]---
> > 
> > Fix it by checking for the successfull initialisation of kvm_arm_init()
> > in finalize_pkvm() before proceeding any futher.
> > 
> > Fixes: 87727ba2bb05 ("KVM: arm64: Ensure CPU PMU probes before pKVM host de-privilege")
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Marc Zyngier <maz@xxxxxxxxxx>
> > Cc: Oliver Upton <oliver.upton@xxxxxxxxx>
> > Cc: James Morse <james.morse@xxxxxxx>
> > Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > Cc: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> 
> I really dislike the additional helper, but now that the capabilities
> are patched, I can't see another way to achieve this so:
>

Yes, I too don't like it and was almost tempted to post it as RFC, but then
I didn't want it to get ignored ;) as it a bug I hit on my setup with
mismatched FF-A version.

> Acked-by: Marc Zyngier <maz@xxxxxxxxxx>
>

Thanks!

-- 
Regards,
Sudeep