KVM: PPC: Book3S HV: Make virtual processor area registration more robust

The PAPR API allows three sorts of per-virtual-processor areas to be
registered (VPA, SLB shadow buffer, and dispatch trace log), and
furthermore, these can be registered and unregistered for another
virtual CPU.  Currently we just update the vcpu fields pointing to
these areas at the time of registration or unregistration.  If this
is done on another vcpu, there is the possibility that the target vcpu
is using those fields at the time and could end up using a bogus
pointer and corrupting memory.

This fixes the race by making the target cpu itself do the update, so
we can be sure that the update happens at a time when the fields
aren't being used.  Each area now has a struct kvmppc_vpa which is
used to manage these updates.  There is also a spinlock which protects
access to all of the kvmppc_vpa structs, other than to the pinned_addr
fields.  (We could have just taken the spinlock when using the vpa,
slb_shadow or dtl fields, but that would mean taking the spinlock on
every guest entry and exit.)

This also changes 'struct dtl' (which was undefined) to 'struct dtl_entry',
which is what the rest of the kernel uses.

Thanks to Michael Ellerman <michael@ellerman.id.au> for pointing out
the need to initialize vcpu->arch.vpa_update_lock.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
index 1c324ff55ea8..318bac9f8752 100644
--- a/arch/powerpc/include/asm/hvcall.h
+++ b/arch/powerpc/include/asm/hvcall.h
@@ -114,6 +114,16 @@
 #define H_PP1			(1UL<<(63-62))
 #define H_PP2			(1UL<<(63-63))
 
+/* Flags for H_REGISTER_VPA subfunction field */
+#define H_VPA_FUNC_SHIFT	(63-18)	/* Bit posn of subfunction code */
+#define H_VPA_FUNC_MASK		7UL
+#define H_VPA_REG_VPA		1UL	/* Register Virtual Processor Area */
+#define H_VPA_REG_DTL		2UL	/* Register Dispatch Trace Log */
+#define H_VPA_REG_SLB		3UL	/* Register SLB shadow buffer */
+#define H_VPA_DEREG_VPA		5UL	/* Deregister Virtual Processor Area */
+#define H_VPA_DEREG_DTL		6UL	/* Deregister Dispatch Trace Log */
+#define H_VPA_DEREG_SLB		7UL	/* Deregister SLB shadow buffer */
+
 /* VASI States */
 #define H_VASI_INVALID          0
 #define H_VASI_ENABLED          1