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authorPeter Zijlstra <peterz@infradead.org>2016-12-08 16:42:15 +0100
committerIngo Molnar <mingo@kernel.org>2016-12-11 13:09:20 +0100
commit11f254dbb3a2e3f0d8552d0dd37f4faa432b6b16 (patch)
tree97eb803fa0c78684a3b4ce488a70af1dfc0abed4 /net/core
parentx86/paravirt: Fix native_patch() (diff)
downloadlinux-11f254dbb3a2e3f0d8552d0dd37f4faa432b6b16.tar.xz
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x86/paravirt: Fix bool return type for PVOP_CALL()
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. Reported-by: kernel test robot <xiaolong.ye@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alok Kataria <akataria@vmware.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Chris Wright <chrisw@sous-sol.org> Cc: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Peter Anvin <hpa@zytor.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: 3cded4179481 ("x86/paravirt: Optimize native pv_lock_ops.vcpu_is_preempted()") Link: http://lkml.kernel.org/r/20161208154349.346057680@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'net/core')
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