From: Michael Ellerman mpe@ellerman.id.au
commit e4e8bc1df691ba5ba749d1e2b67acf9827e51a35 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kvm/book3s_64_mmu_host.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/powerpc/kvm/book3s_64_mmu_host.c +++ b/arch/powerpc/kvm/book3s_64_mmu_host.c @@ -12,6 +12,7 @@ #include <asm/kvm_ppc.h> #include <asm/kvm_book3s.h> #include <asm/book3s/64/mmu-hash.h> +#include <asm/book3s/64/pkeys.h> #include <asm/machdep.h> #include <asm/mmu_context.h> #include <asm/hw_irq.h> @@ -133,6 +134,7 @@ int kvmppc_mmu_map_page(struct kvm_vcpu else kvmppc_mmu_flush_icache(pfn);
+ rflags |= pte_to_hpte_pkey_bits(0, HPTE_USE_KERNEL_KEY); rflags = (rflags & ~HPTE_R_WIMG) | orig_pte->wimg;
/*