e4e8bc1df6
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 b2ff33a10c8b ("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: d94b827e89dc ("powerpc/book3s64/kuap: Use Key 3 for kernel mapping with hash translation")
Cc: stable@vger.kernel.org # v5.11+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210419120139.1455937-1-mpe@ellerman.id.au
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.