[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF
Hi, attached patch corrects a bug in cmpxchg emulation in the hypervisor. BS2000 running as HVM-domain on 4 vcpus (no HAP) hit an error due to this bug after several days. Juergen -- Juergen Gross Principal Developer Operating Systems TSP ES&S SWE OS6 Telephone: +49 (0) 89 636 47950 Fujitsu Technolgy Solutions e-mail: juergen.gross@xxxxxxxxxxxxxx Otto-Hahn-Ring 6 Internet: ts.fujitsu.com D-81739 Muenchen Company details: ts.fujitsu.com/imprint.html The cmpxchg emulation for accesses to page tables of guests doesn't handle races correct. ops->cmpxchg might return X86EMUL_CMPXCHG_FAILED if the addressed memory location changed after checking the old contents. In this case ZF was not changed and could remain 1 instead of being set to 0. Signed-off-by: juergen.gross@xxxxxxxxxxxxxx # HG changeset patch # User juergen.gross@xxxxxxxxxxxxxx # Date 1249540842 -7200 # Node ID 26adbdb6cb1d59d95e0a65b6a0d38fa8e95b9f51 # Parent 68e8b8379244e293c55875e7dc3692fc81d3d212 handle race on cmpxchg emulation diff -r 68e8b8379244 -r 26adbdb6cb1d xen/arch/x86/x86_emulate/x86_emulate.c --- a/xen/arch/x86/x86_emulate/x86_emulate.c Sun Aug 02 13:43:15 2009 +0100 +++ b/xen/arch/x86/x86_emulate/x86_emulate.c Thu Aug 06 08:40:42 2009 +0200 @@ -4124,6 +4124,7 @@ op_bytes *= 2; /* Get actual old value. */ +cmpxchg_failed: for ( i = 0; i < (op_bytes/sizeof(long)); i++ ) if ( (rc = read_ulong(ea.mem.seg, ea.mem.off + i*sizeof(long), &old[i], sizeof(long), ctxt, ops)) != 0 ) @@ -4151,10 +4152,13 @@ else { /* Expected == actual: attempt atomic cmpxchg and set ZF. */ - if ( (rc = ops->cmpxchg(ea.mem.seg, ea.mem.off, old, - new, op_bytes, ctxt)) != 0 ) - goto done; - _regs.eflags |= EFLG_ZF; + rc = ops->cmpxchg(ea.mem.seg, ea.mem.off, old, new, op_bytes, ctxt); + if ( rc == 0 ) + _regs.eflags |= EFLG_ZF; + else if ( rc == X86EMUL_CMPXCHG_FAILED ) + goto cmpxchg_failed; + else + goto done; } break; } _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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