sparc64: Fix tsb_grow() in atomic context.

If our first THP installation for an MM is via the set_pmd_at() done
during khugepaged's collapsing we'll end up in tsb_grow() trying to do
a GFP_KERNEL allocation with several locks held.

Simply using GFP_ATOMIC in this situation is not the best option
because we really can't have this fail, so we'd really like to keep
this an order 0 GFP_KERNEL allocation if possible.

Also, doing the TSB allocation from khugepaged is a really bad idea
because we'll allocate it potentially from the wrong NUMA node in that
context.

So what we do is defer the hugepage TSB allocation until the first TLB
miss we take on a hugepage.  This is slightly tricky because we have
to handle two unusual cases:

1) Taking the first hugepage TLB miss in the window trap handler.
   We'll call the winfix_trampoline when that is detected.

2) An initial TSB allocation via TLB miss races with a hugetlb
   fault on another cpu running the same MM.  We handle this by
   unconditionally loading the TSB we see into the current cpu
   even if it's non-NULL at hugetlb_setup time.

Reported-by: Meelis Roos <mroos@ut.ee>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 35 insertions, 4 deletions

diff --git a/arch/sparc/kernel/tsb.S b/arch/sparc/kernel/tsb.S
index d4bdc7a62375..a313e4a9399b 100644
--- a/arch/sparc/kernel/tsb.S
+++ b/arch/sparc/kernel/tsb.S
@@ -136,12 +136,43 @@ tsb_miss_page_table_walk_sun4v_fastpath:
          nop
 
         /* It is a huge page, use huge page TSB entry address we
-         * calculated above.
+         * calculated above.  If the huge page TSB has not been
+         * allocated, setup a trap stack and call hugetlb_setup()
+         * to do so, then return from the trap to replay the TLB
+         * miss.
+         *
+         * This is necessary to handle the case of transparent huge
+         * pages where we don't really have a non-atomic context
+         * in which to allocate the hugepage TSB hash table.  When
+         * the 'mm' faults in the hugepage for the first time, we
+         * thus handle it here.  This also makes sure that we can
+         * allocate the TSB hash table on the correct NUMA node.
          */
         TRAP_LOAD_TRAP_BLOCK(%g7, %g2)
-        ldx             [%g7 + TRAP_PER_CPU_TSB_HUGE_TEMP], %g2
-        cmp             %g2, -1
-        movne           %xcc, %g2, %g1
+        ldx             [%g7 + TRAP_PER_CPU_TSB_HUGE_TEMP], %g1
+        cmp             %g1, -1
+        bne,pt          %xcc, 60f
+         nop
+
+661:    rdpr            %pstate, %g5
+        wrpr            %g5, PSTATE_AG | PSTATE_MG, %pstate
+        .section        .sun4v_2insn_patch, "ax"
+        .word           661b
+        SET_GL(1)
+        nop
+        .previous
+
+        rdpr    %tl, %g3
+        cmp     %g3, 1
+        bne,pn  %xcc, winfix_trampoline
+         nop
+        ba,pt   %xcc, etrap
+         rd     %pc, %g7
+        call    hugetlb_setup
+         add    %sp, PTREGS_OFF, %o0
+        ba,pt   %xcc, rtrap
+         nop
+
 60:
 #endif