diff options
authorRob Gardner <rob.gardner@oracle.com>2017-07-17 09:22:27 -0600
committerDavid S. Miller <davem@davemloft.net>2017-07-18 11:25:52 -0700
commitfc290a114fc6034b0f6a5a46e2fb7d54976cf87a (patch)
parentMerge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc (diff)
sparc64: Prevent perf from running during super critical sections
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); ... load_secondary_context(mm); tsb_context_switch(mm); ... 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.aldridge@oracle.com> Signed-off-by: Rob Gardner <rob.gardner@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
3 files changed, 22 insertions, 7 deletions
diff --git a/arch/sparc/include/asm/mmu_context_64.h b/arch/sparc/include/asm/mmu_context_64.h
index 2cddcda4f85f..87841d687f8d 100644
--- 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 *mm);
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(struct mm_struct *mm)
- , __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_struct *old_mm, struct mm_struct *mm, str
* 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
diff --git a/arch/sparc/kernel/tsb.S b/arch/sparc/kernel/tsb.S
index 07c0df924960..db872dbfafe9 100644
--- 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
+661: stxa %o4, [%o5] ASI_DMMU
+ .section .sun4v_1insn_patch, "ax"
+ .word 661b
+ stxa %o4, [%o5] ASI_MMU
+ .previous
+ flush %g6
stx %o0, [%g2 + TRAP_PER_CPU_PGD_PADDR]
diff --git a/arch/sparc/power/hibernate.c b/arch/sparc/power/hibernate.c
index 17bd2e167e07..df707a8ad311 100644
--- 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));