KVM: PPC: Book3S HV: Synthesize segment fault if SLB lookup fails

When handling a hypervisor data or instruction storage interrupt (HDSI
or HISI), we look up the SLB entry for the address being accessed in
order to translate the effective address to a virtual address which can
be looked up in the guest HPT.  This lookup can occasionally fail due
to the guest replacing an SLB entry without invalidating the evicted
SLB entry.  In this situation an ERAT (effective to real address
translation cache) entry can persist and be used by the hardware even
though there is no longer a corresponding SLB entry.

Previously we would just deliver a data or instruction storage interrupt
(DSI or ISI) to the guest in this case.  However, this is not correct
and has been observed to cause guests to crash, typically with a
data storage protection interrupt on a store to the vmemmap area.

Instead, what we do now is to synthesize a data or instruction segment
interrupt.  That should cause the guest to reload an appropriate entry
into the SLB and retry the faulting instruction.  If it still faults,
we should find an appropriate SLB entry next time and be able to handle
the fault.

Tested-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 12 insertions, 8 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index b1dab8d1d885..3c6badcd53ef 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -1749,7 +1749,8 @@ kvmppc_hdsi:
         beq     3f
         clrrdi  r0, r4, 28
         PPC_SLBFEE_DOT(R5, R0)          /* if so, look up SLB */
-        bne     1f                      /* if no SLB entry found */
+        li      r0, BOOK3S_INTERRUPT_DATA_SEGMENT
+        bne     7f                      /* if no SLB entry found */
 4:      std     r4, VCPU_FAULT_DAR(r9)
         stw     r6, VCPU_FAULT_DSISR(r9)
 
@@ -1768,14 +1769,15 @@ kvmppc_hdsi:
         cmpdi   r3, -2                  /* MMIO emulation; need instr word */
         beq     2f
 
-        /* Synthesize a DSI for the guest */
+        /* Synthesize a DSI (or DSegI) for the guest */
         ld      r4, VCPU_FAULT_DAR(r9)
         mr      r6, r3
-1:      mtspr   SPRN_DAR, r4
+1:      li      r0, BOOK3S_INTERRUPT_DATA_STORAGE
         mtspr   SPRN_DSISR, r6
+7:      mtspr   SPRN_DAR, r4
         mtspr   SPRN_SRR0, r10
         mtspr   SPRN_SRR1, r11
-        li      r10, BOOK3S_INTERRUPT_DATA_STORAGE
+        mr      r10, r0
         bl      kvmppc_msr_interrupt
 fast_interrupt_c_return:
 6:      ld      r7, VCPU_CTR(r9)
@@ -1823,7 +1825,8 @@ kvmppc_hisi:
         beq     3f
         clrrdi  r0, r10, 28
         PPC_SLBFEE_DOT(R5, R0)          /* if so, look up SLB */
-        bne     1f                      /* if no SLB entry found */
+        li      r0, BOOK3S_INTERRUPT_INST_SEGMENT
+        bne     7f                      /* if no SLB entry found */
 4:
         /* Search the hash table. */
         mr      r3, r9                  /* vcpu pointer */
@@ -1840,11 +1843,12 @@ kvmppc_hisi:
         cmpdi   r3, -1                  /* handle in kernel mode */
         beq     guest_exit_cont
 
-        /* Synthesize an ISI for the guest */
+        /* Synthesize an ISI (or ISegI) for the guest */
         mr      r11, r3
-1:      mtspr   SPRN_SRR0, r10
+1:      li      r0, BOOK3S_INTERRUPT_INST_STORAGE
+7:      mtspr   SPRN_SRR0, r10
         mtspr   SPRN_SRR1, r11
-        li      r10, BOOK3S_INTERRUPT_INST_STORAGE
+        mr      r10, r0
         bl      kvmppc_msr_interrupt
         b       fast_interrupt_c_return