Re: [Qemu-devel] [PATCH 2/2] target-ppc: Eliminate kvmppc_kern_htab global

[Thomas Huth <thuth@redhat.com>]

On 04.03.2016 06:35, David Gibson wrote:
> fa48b43 "target-ppc: Remove hack for ppc_hash64_load_hpte*() with HV KVM"
> purports to remove a hack in the handling of hash page tables (HPTs)
> managed by KVM instead of qemu.  However, it actually went in the wrong
> direction.
> 
> That patch requires anything looking for an external HPT (that is one not
> managed by the guest itself) to check both env->external_htab (for a qemu
> managed HPT) and kvmppc_kern_htab (for a KVM managed HPT).  That's a
> problem because kvmppc_kern_htab is local to mmu-hash64.c, but some places
> which need to check for an external HPT are outside that, such as
> kvm_arch_get_registers().  The latter was subtly broken by the earlier
> patch such that gdbstub can no longer access memory.
> 
> Basically a KVM managed HPT is much more like a qemu managed HPT than it is
> like a guest managed HPT, so the original "hack" was actually on the right
> track.
> 
> This partially reverts fa48b43, so we again mark a KVM managed external HPT
> by putting a special but non-NULL value in env->external_htab.  It then
> goes further, using that marker to eliminate the kvmppc_kern_htab global
> entirely.  The ppc_hash64_set_external_hpt() helper function is extended
> to set that marker if passed a NULL value (if you're setting an external
> HPT, but don't have an actual HPT to set, the assumption is that it must
> be a KVM managed HPT).
> 
> This also has some flow-on changes to the HPT access helpers, required by
> the above changes.
> 
> Reported-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  hw/ppc/spapr.c          |  3 +--
>  hw/ppc/spapr_hcall.c    | 10 +++++-----
>  target-ppc/mmu-hash64.c | 40 ++++++++++++++++++----------------------
>  target-ppc/mmu-hash64.h |  9 +++------
>  4 files changed, 27 insertions(+), 35 deletions(-)

Patch looks fine to me.

Reviewed-by: Thomas Huth <thuth@redhat.com>