path: root/arch
diff options
authorStephan Schreiber <info@fs-driver.org>2013-03-19 15:27:12 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-05-07 20:33:09 -0700
commited34a28717d40623fbd1f8952db408f8ad5f06aa (patch)
tree532f571ab1c0ad1cef7c512e328a6153c4c4c546 /arch
parent7b5b8170ad72d45e853d5cf96c1c0c7dbb0474dd (diff)
Wrong asm register contraints in the kvm implementation
commit de53e9caa4c6149ef4a78c2f83d7f5b655848767 upstream. The Linux Kernel contains some inline assembly source code which has wrong asm register constraints in arch/ia64/kvm/vtlb.c. I observed this on Kernel 3.2.35 but it is also true on the most recent Kernel 3.9-rc1. File arch/ia64/kvm/vtlb.c: u64 guest_vhpt_lookup(u64 iha, u64 *pte) { u64 ret; struct thash_data *data; data = __vtr_lookup(current_vcpu, iha, D_TLB); if (data != NULL) thash_vhpt_insert(current_vcpu, data->page_flags, data->itir, iha, D_TLB); asm volatile ( "rsm psr.ic|psr.i;;" "srlz.d;;" "ld8.s r9=[%1];;" "tnat.nz p6,p7=r9;;" "(p6) mov %0=1;" "(p6) mov r9=r0;" "(p7) extr.u r9=r9,0,53;;" "(p7) mov %0=r0;" "(p7) st8 [%2]=r9;;" "ssm psr.ic;;" "srlz.d;;" "ssm psr.i;;" "srlz.d;;" : "=r"(ret) : "r"(iha), "r"(pte):"memory"); return ret; } The list of output registers is : "=r"(ret) : "r"(iha), "r"(pte):"memory"); The constraint "=r" means that the GCC has to maintain that these vars are in registers and contain valid info when the program flow leaves the assembly block (output registers). But "=r" also means that GCC can put them in registers that are used as input registers. Input registers are iha, pte on the example. If the predicate p7 is true, the 8th assembly instruction "(p7) mov %0=r0;" is the first one which writes to a register which is maintained by the register constraints; it sets %0. %0 means the first register operand; it is ret here. This instruction might overwrite the %2 register (pte) which is needed by the next instruction: "(p7) st8 [%2]=r9;;" Whether it really happens depends on how GCC decides what registers it uses and how it optimizes the code. The attached patch fixes the register operand constraints in arch/ia64/kvm/vtlb.c. The register constraints should be : "=&r"(ret) : "r"(iha), "r"(pte):"memory"); The & means that GCC must not use any of the input registers to place this output register in. This is Debian bug#702639 (http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=702639). The patch is applicable on Kernel 3.9-rc1, 3.2.35 and many other versions. Signed-off-by: Stephan Schreiber <info@fs-driver.org> Signed-off-by: Tony Luck <tony.luck@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/ia64/kvm/vtlb.c b/arch/ia64/kvm/vtlb.c
index 4332f7ee520..a7869f8f49a 100644
--- a/arch/ia64/kvm/vtlb.c
+++ b/arch/ia64/kvm/vtlb.c
@@ -256,7 +256,7 @@ u64 guest_vhpt_lookup(u64 iha, u64 *pte)
"ssm psr.i;;"
- : "=r"(ret) : "r"(iha), "r"(pte):"memory");
+ : "=&r"(ret) : "r"(iha), "r"(pte) : "memory");
return ret;