On 14.03.2012, at 08:52, Benjamin Herrenschmidt wrote:
> 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@xxxxxxxxxxxxxxxxxxx>
> ---
>
> Avi, please consider merging ASAP as this is a fairly annoying
> bug and the fix is reasonably obvious.
>
> arch/powerpc/kvm/book3s.c | 3 +++
> arch/powerpc/kvm/book3s_pr.c | 17 +++++++++++++++++
> 2 files changed, 20 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
> index e41ac6f..34487d4 100644
> --- a/arch/powerpc/kvm/book3s.c
> +++ b/arch/powerpc/kvm/book3s.c
> @@ -289,6 +289,9 @@ pfn_t kvmppc_gfn_to_pfn(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;
> +
> /* Magic page override */
> if (unlikely(mp_pa) &&
> unlikely(((gfn << PAGE_SHIFT) & KVM_PAM) ==
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index d6851a1..23919d4 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -137,6 +137,20 @@ 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 (!(old_msr & MSR_PR) && !(old_msr & MSR_SF) && (msr & MSR_SF)) {
This should also check if we're using a magic page at all. I've added that check and replaced my patch with yours in kvm-ppc-next.
Alex
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