* [PATCH 1/2] x86,paravirt: Fix native_patch()
2016-12-08 15:42 [PATCH 0/2] Fix paravirt fail Peter Zijlstra
@ 2016-12-08 15:42 ` Peter Zijlstra
2016-12-08 15:42 ` [PATCH 2/2] x86, paravirt: Fix bool return type for PVOP_CALL Peter Zijlstra
1 sibling, 0 replies; 5+ messages in thread
From: Peter Zijlstra @ 2016-12-08 15:42 UTC (permalink / raw)
To: linux-kernel, x86
Cc: Jeremy Fitzhardinge, Peter Zijlstra (Intel), Pan Xinhui,
Alok Kataria, kernel test robot, virtualization, Chris Wright,
Borislav Petkov, Peter Anvin, Paolo Bonzini, Thomas Gleixner,
Ingo Molnar
[-- Attachment #1: peter_zijlstra-fd6f48529f-_aim7_jobs-per-min_-26_1__regression.patch --]
[-- Type: text/plain, Size: 1713 bytes --]
While chasing a regression I noticed we potentially patch the wrong
code in native_patch().
If we do not select the native code sequence, we must use the default
patcher, not fall-through the switch case.
Fixes: 3cded4179481 ("x86/paravirt: Optimize native pv_lock_ops.vcpu_is_preempted()")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/paravirt_patch_32.c | 4 ++++
arch/x86/kernel/paravirt_patch_64.c | 4 ++++
2 files changed, 8 insertions(+)
--- a/arch/x86/kernel/paravirt_patch_32.c
+++ b/arch/x86/kernel/paravirt_patch_32.c
@@ -56,15 +56,19 @@ unsigned native_patch(u8 type, u16 clobb
end = end_pv_lock_ops_queued_spin_unlock;
goto patch_site;
}
+ goto patch_default;
+
case PARAVIRT_PATCH(pv_lock_ops.vcpu_is_preempted):
if (pv_is_native_vcpu_is_preempted()) {
start = start_pv_lock_ops_vcpu_is_preempted;
end = end_pv_lock_ops_vcpu_is_preempted;
goto patch_site;
}
+ goto patch_default;
#endif
default:
+patch_default:
ret = paravirt_patch_default(type, clobbers, ibuf, addr, len);
break;
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -68,15 +68,19 @@ unsigned native_patch(u8 type, u16 clobb
end = end_pv_lock_ops_queued_spin_unlock;
goto patch_site;
}
+ goto patch_default;
+
case PARAVIRT_PATCH(pv_lock_ops.vcpu_is_preempted):
if (pv_is_native_vcpu_is_preempted()) {
start = start_pv_lock_ops_vcpu_is_preempted;
end = end_pv_lock_ops_vcpu_is_preempted;
goto patch_site;
}
+ goto patch_default;
#endif
default:
+patch_default:
ret = paravirt_patch_default(type, clobbers, ibuf, addr, len);
break;
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH 2/2] x86, paravirt: Fix bool return type for PVOP_CALL
2016-12-08 15:42 [PATCH 0/2] Fix paravirt fail Peter Zijlstra
2016-12-08 15:42 ` [PATCH 1/2] x86,paravirt: Fix native_patch() Peter Zijlstra
@ 2016-12-08 15:42 ` Peter Zijlstra
2016-12-08 16:40 ` Pan Xinhui
1 sibling, 1 reply; 5+ messages in thread
From: Peter Zijlstra @ 2016-12-08 15:42 UTC (permalink / raw)
To: linux-kernel, x86
Cc: Jeremy Fitzhardinge, Peter Zijlstra (Intel), Pan Xinhui,
Alok Kataria, kernel test robot, virtualization, Chris Wright,
Borislav Petkov, Peter Anvin, Paolo Bonzini, Thomas Gleixner,
Ingo Molnar
[-- Attachment #1: peterz-fix-paravirt-bool.patch --]
[-- Type: text/plain, Size: 2945 bytes --]
Commit 3cded4179481 ("x86/paravirt: Optimize native
pv_lock_ops.vcpu_is_preempted()") introduced a paravirt op with bool
return type [*]
It turns out that the PVOP_CALL*() macros miscompile when rettype is
bool. Code that looked like:
83 ef 01 sub $0x1,%edi
ff 15 32 a0 d8 00 callq *0xd8a032(%rip) # ffffffff81e28120 <pv_lock_ops+0x20>
84 c0 test %al,%al
ended up looking like so after PVOP_CALL1() was applied:
83 ef 01 sub $0x1,%edi
48 63 ff movslq %edi,%rdi
ff 14 25 20 81 e2 81 callq *0xffffffff81e28120
48 85 c0 test %rax,%rax
Note how it tests the whole of %rax, even though a typical bool return
function only sets %al, like:
0f 95 c0 setne %al
c3 retq
This is because ____PVOP_CALL() does:
__ret = (rettype)__eax;
and while regular integer type casts truncate the result, a cast to
bool tests for any !0 value. Fix this by explicitly truncating to
sizeof(rettype) before casting.
[*] The actual bug should've been exposed in commit 446f3dc8cc0a
("locking/core, x86/paravirt: Implement vcpu_is_preempted(cpu) for KVM
and Xen guests") but that didn't properly implement the paravirt call.
Cc: Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: virtualization@lists.linux-foundation.org
Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Fixes: 3cded4179481 ("x86/paravirt: Optimize native pv_lock_ops.vcpu_is_preempted()")
Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/paravirt_types.h | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -508,6 +508,18 @@ int paravirt_disable_iospace(void);
#define PVOP_TEST_NULL(op) ((void)op)
#endif
+#define PVOP_RETMASK(rettype) \
+ ({ unsigned long __mask = ~0UL; \
+ switch (sizeof(rettype)) { \
+ case 1: __mask = 0xffUL; break; \
+ case 2: __mask = 0xffffUL; break; \
+ case 4: __mask = 0xffffffffUL; break; \
+ default: break; \
+ } \
+ __mask; \
+ })
+
+
#define ____PVOP_CALL(rettype, op, clbr, call_clbr, extra_clbr, \
pre, post, ...) \
({ \
@@ -535,7 +547,7 @@ int paravirt_disable_iospace(void);
paravirt_clobber(clbr), \
##__VA_ARGS__ \
: "memory", "cc" extra_clbr); \
- __ret = (rettype)__eax; \
+ __ret = (rettype)(__eax & PVOP_RETMASK(rettype)); \
} \
__ret; \
})
^ permalink raw reply [flat|nested] 5+ messages in thread