1. 22 Apr, 2021 23 commits
  2. 21 Apr, 2021 16 commits
  3. 20 Apr, 2021 1 commit
    • Michael Ellerman's avatar
      powerpc/kvm: Fix PR KVM with KUAP/MEM_KEYS enabled · e4e8bc1d
      Michael Ellerman authored
      The changes to add KUAP support with the hash MMU broke booting of KVM
      PR guests. The symptom is no visible progress of the guest, or possibly
      just "SLOF" being printed to the qemu console.
      
      Host code is still executing, but breaking into xmon might show a stack
      trace such as:
      
        __might_fault+0x84/0xe0 (unreliable)
        kvm_read_guest+0x1c8/0x2f0 [kvm]
        kvmppc_ld+0x1b8/0x2d0 [kvm]
        kvmppc_load_last_inst+0x50/0xa0 [kvm]
        kvmppc_exit_pr_progint+0x178/0x220 [kvm_pr]
        kvmppc_handle_exit_pr+0x31c/0xe30 [kvm_pr]
        after_sprg3_load+0x80/0x90 [kvm_pr]
        kvmppc_vcpu_run_pr+0x104/0x260 [kvm_pr]
        kvmppc_vcpu_run+0x34/0x48 [kvm]
        kvm_arch_vcpu_ioctl_run+0x340/0x450 [kvm]
        kvm_vcpu_ioctl+0x2ac/0x8c0 [kvm]
        sys_ioctl+0x320/0x1060
        system_call_exception+0x160/0x270
        system_call_common+0xf0/0x27c
      
      Bisect points to commit b2ff33a1 ("powerpc/book3s64/hash/kuap:
      Enable kuap on hash"), but that's just the commit that enabled KUAP with
      hash and made the bug visible.
      
      The root cause seems to be that KVM PR is creating kernel mappings that
      don't use the correct key, since we switched to using key 3.
      
      We have a helper for adding the right key value, however it's designed
      to take a pteflags variable, which the KVM code doesn't have. But we can
      make it work by passing 0 for the pteflags, and tell it explicitly that
      it should use the kernel key.
      
      With that changed guests boot successfully.
      
      Fixes: d94b827e ("powerpc/book3s64/kuap: Use Key 3 for kernel mapping with hash translation")
      Cc: stable@vger.kernel.org # v5.11+
      Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
      Link: https://lore.kernel.org/r/20210419120139.1455937-1-mpe@ellerman.id.au
      e4e8bc1d