From: Rob Gardner <rob.gardner@oracle.com>
Date: Mon, 17 Jul 2017 09:22:27 -0600
Subject: [PATCH] sparc64: Prevent perf from running during super critical
sections
References: bnc#1060662
Patch-mainline: 4.12.6
Git-commit: fc290a114fc6034b0f6a5a46e2fb7d54976cf87a
[ 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);
...
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
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(-)
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)
{
__tsb_context_switch(__pa(mm->pgd),
&mm->context.tsb_block[MM_TSB_BASE],
@@ -40,9 +42,12 @@ static inline void tsb_context_switch(struct mm_struct *mm)
#else
NULL
#endif
- , __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
+ 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
+
+1:
TRAP_LOAD_TRAP_BLOCK(%g2, %g3)
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));
}
--
2.14.2