4.12-stable review patch.  If anyone has any objections, please let me know.


From: Rob Gardner <rob.gard...@oracle.com>

[ Upstream commit fc290a114fc6034b0f6a5a46e2fb7d54976cf87a ]

This fixes another cause of random segfaults and bus errors that may
occur while running perf with the callgraph option.

Critical sections beginning with spin_lock_irqsave() raise the interrupt
level to PIL_NORMAL_MAX (14) and intentionally do not block performance
counter interrupts, which arrive at PIL_NMI (15).

But some sections of code are "super critical" with respect to perf
because the perf_callchain_user() path accesses user space and may cause
TLB activity as well as faults as it unwinds the user stack.

One particular critical section occurs in switch_mm:

        spin_lock_irqsave(&mm->context.lock, flags);
        spin_unlock_irqrestore(&mm->context.lock, flags);

If a perf interrupt arrives in between load_secondary_context() and
tsb_context_switch(), then perf_callchain_user() could execute with
the context ID of one process, but with an active TSB for a different
process. When the user stack is accessed, it is very likely to
incur a TLB miss, since the h/w context ID has been changed. The TLB
will then be reloaded with a translation from the TSB for one process,
but using a context ID for another process. This exposes memory from
one process to another, and since it is a mapping for stack memory,
this usually causes the new process to crash quickly.

This super critical section needs more protection than is provided
by spin_lock_irqsave() since perf interrupts must not be allowed in.

Since __tsb_context_switch already goes through the trouble of
disabling interrupts completely, we fix this by moving the secondary
context load down into this better protected region.

Orabug: 25577560

Signed-off-by: Dave Aldridge <david.j.aldri...@oracle.com>
Signed-off-by: Rob Gardner <rob.gard...@oracle.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
 arch/sparc/include/asm/mmu_context_64.h |   14 +++++++++-----
 arch/sparc/kernel/tsb.S                 |   12 ++++++++++++
 arch/sparc/power/hibernate.c            |    3 +--
 3 files changed, 22 insertions(+), 7 deletions(-)

--- a/arch/sparc/include/asm/mmu_context_64.h
+++ b/arch/sparc/include/asm/mmu_context_64.h
@@ -27,9 +27,11 @@ void destroy_context(struct mm_struct *m
 void __tsb_context_switch(unsigned long pgd_pa,
                          struct tsb_config *tsb_base,
                          struct tsb_config *tsb_huge,
-                         unsigned long tsb_descr_pa);
+                         unsigned long tsb_descr_pa,
+                         unsigned long secondary_ctx);
-static inline void tsb_context_switch(struct mm_struct *mm)
+static inline void tsb_context_switch_ctx(struct mm_struct *mm,
+                                         unsigned long ctx)
@@ -40,9 +42,12 @@ static inline void tsb_context_switch(st
-                            , __pa(&mm->context.tsb_descr[MM_TSB_BASE]));
+                            , __pa(&mm->context.tsb_descr[MM_TSB_BASE]),
+                            ctx);
+#define tsb_context_switch(X) tsb_context_switch_ctx(X, 0)
 void tsb_grow(struct mm_struct *mm,
              unsigned long tsb_index,
              unsigned long mm_rss);
@@ -112,8 +117,7 @@ static inline void switch_mm(struct mm_s
         * cpu0 to update it's TSB because at that point the cpu_vm_mask
         * only had cpu1 set in it.
-       load_secondary_context(mm);
-       tsb_context_switch(mm);
+       tsb_context_switch_ctx(mm, CTX_HWBITS(mm->context));
        /* Any time a processor runs a context on an address space
         * for the first time, we must flush that context out of the
--- a/arch/sparc/kernel/tsb.S
+++ b/arch/sparc/kernel/tsb.S
@@ -360,6 +360,7 @@ tsb_flush:
         * %o1: TSB base config pointer
         * %o2: TSB huge config pointer, or NULL if none
         * %o3: Hypervisor TSB descriptor physical address
+        * %o4: Secondary context to load, if non-zero
         * We have to run this whole thing with interrupts
         * disabled so that the current cpu doesn't change
@@ -372,6 +373,17 @@ __tsb_context_switch:
        rdpr    %pstate, %g1
        wrpr    %g1, PSTATE_IE, %pstate
+       brz,pn  %o4, 1f
+        mov    SECONDARY_CONTEXT, %o5
+661:   stxa    %o4, [%o5] ASI_DMMU
+       .section .sun4v_1insn_patch, "ax"
+       .word   661b
+       stxa    %o4, [%o5] ASI_MMU
+       .previous
+       flush   %g6
        TRAP_LOAD_TRAP_BLOCK(%g2, %g3)
        stx     %o0, [%g2 + TRAP_PER_CPU_PGD_PADDR]
--- a/arch/sparc/power/hibernate.c
+++ b/arch/sparc/power/hibernate.c
@@ -35,6 +35,5 @@ void restore_processor_state(void)
        struct mm_struct *mm = current->active_mm;
-       load_secondary_context(mm);
-       tsb_context_switch(mm);
+       tsb_context_switch_ctx(mm, CTX_HWBITS(mm->context));

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