powerpc/kvm: Fix magic page vs. 32-bit RTAS on ppc64

When the kernel calls into RTAS, it switches to 32-bit mode. The
magic page was is longer accessible in that case, causing the
patched instructions in the RTAS call wrapper to crash.

This fixes it by making available a 32-bit mapping of the magic
page in that case. This mapping is flushed whenever we switch
the kernel back to 64-bit mode.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[agraf: add a check if the magic page is mapped]
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 912e10fbf6ef..dba282e5093f 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -145,6 +145,21 @@ void kvmppc_set_msr(struct kvm_vcpu *vcpu, u64 msr)
                 }
         }
 
+        /*
+         * When switching from 32 to 64-bit, we may have a stale 32-bit
+         * magic page around, we need to flush it. Typically 32-bit magic
+         * page will be instanciated when calling into RTAS. Note: We
+         * assume that such transition only happens while in kernel mode,
+         * ie, we never transition from user 32-bit to kernel 64-bit with
+         * a 32-bit magic page around.
+         */
+        if (vcpu->arch.magic_page_pa &&
+            !(old_msr & MSR_PR) && !(old_msr & MSR_SF) && (msr & MSR_SF)) {
+                /* going from RTAS to normal kernel code */
+                kvmppc_mmu_pte_flush(vcpu, (uint32_t)vcpu->arch.magic_page_pa,
+                                     ~0xFFFUL);
+        }
+
         /* Preload FPU if it's enabled */
         if (vcpu->arch.shared->msr & MSR_FP)
                 kvmppc_handle_ext(vcpu, BOOK3S_INTERRUPT_FP_UNAVAIL, MSR_FP);
@@ -252,6 +267,9 @@ static int kvmppc_visible_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
 {
         ulong mp_pa = vcpu->arch.magic_page_pa;
 
+        if (!(vcpu->arch.shared->msr & MSR_SF))
+                mp_pa = (uint32_t)mp_pa;
+
         if (unlikely(mp_pa) &&
             unlikely((mp_pa & KVM_PAM) >> PAGE_SHIFT == gfn)) {
                 return 1;