File 20031-x86-pmode-load-seg-retry.patch of Package xen
# HG changeset patch
# User Keir Fraser <keir.fraser@citrix.com>
# Date 1249548862 -3600
# Node ID 34bdb5a29963fda7f491c3c145453264c596bdbb
# Parent fb4b7032a9bc9ea44ef7cbb18720795afa113d06
x86_emulate: Remove cmpxchg retry loop from protmode_load_seg().
It is safer to retry in a loop via the caller.
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1011,88 +1011,84 @@ protmode_load_seg(
if ( ((sel & 0xfff8) + 7) > desctab.limit )
goto raise_exn;
- do {
- if ( (rc = read_ulong(x86_seg_none, desctab.base + (sel & 0xfff8),
- &val, 4, ctxt, ops)) )
- return rc;
- desc.a = val;
- if ( (rc = read_ulong(x86_seg_none, desctab.base + (sel & 0xfff8) + 4,
- &val, 4, ctxt, ops)) )
- return rc;
- desc.b = val;
+ if ( (rc = read_ulong(x86_seg_none, desctab.base + (sel & 0xfff8),
+ &val, 4, ctxt, ops)) )
+ return rc;
+ desc.a = val;
+ if ( (rc = read_ulong(x86_seg_none, desctab.base + (sel & 0xfff8) + 4,
+ &val, 4, ctxt, ops)) )
+ return rc;
+ desc.b = val;
- /* Segment present in memory? */
- if ( !(desc.b & (1u<<15)) )
- {
- fault_type = EXC_NP;
- goto raise_exn;
- }
+ /* Segment present in memory? */
+ if ( !(desc.b & (1u<<15)) )
+ {
+ fault_type = EXC_NP;
+ goto raise_exn;
+ }
- if ( !is_x86_user_segment(seg) )
- {
- /* System segments must have S flag == 0. */
- if ( desc.b & (1u << 12) )
- goto raise_exn;
- /* We do not support 64-bit descriptor types. */
- if ( in_longmode(ctxt, ops) )
- return X86EMUL_UNHANDLEABLE;
- }
- /* User segments must have S flag == 1. */
- else if ( !(desc.b & (1u << 12)) )
+ if ( !is_x86_user_segment(seg) )
+ {
+ /* System segments must have S flag == 0. */
+ if ( desc.b & (1u << 12) )
goto raise_exn;
+ /* We do not support 64-bit descriptor types. */
+ if ( in_longmode(ctxt, ops) )
+ return X86EMUL_UNHANDLEABLE;
+ }
+ /* User segments must have S flag == 1. */
+ else if ( !(desc.b & (1u << 12)) )
+ goto raise_exn;
+
+ dpl = (desc.b >> 13) & 3;
+ rpl = sel & 3;
+ cpl = ss.attr.fields.dpl;
- dpl = (desc.b >> 13) & 3;
- rpl = sel & 3;
- cpl = ss.attr.fields.dpl;
-
- switch ( seg )
- {
- case x86_seg_cs:
- /* Code segment? */
- if ( !(desc.b & (1u<<11)) )
- goto raise_exn;
- /* Non-conforming segment: check DPL against RPL. */
- if ( ((desc.b & (6u<<9)) != (6u<<9)) && (dpl != rpl) )
- goto raise_exn;
- break;
- case x86_seg_ss:
- /* Writable data segment? */
- if ( (desc.b & (5u<<9)) != (1u<<9) )
- goto raise_exn;
- if ( (dpl != cpl) || (dpl != rpl) )
- goto raise_exn;
- break;
- case x86_seg_ldtr:
- /* LDT system segment? */
- if ( (desc.b & (15u<<8)) != (2u<<8) )
- goto raise_exn;
- goto skip_accessed_flag;
- case x86_seg_tr:
- /* Available TSS system segment? */
- if ( (desc.b & (15u<<8)) != (9u<<8) )
- goto raise_exn;
- a_flag = 0x200; /* busy flag */
- break;
- default:
- /* Readable code or data segment? */
- if ( (desc.b & (5u<<9)) == (4u<<9) )
- goto raise_exn;
- /* Non-conforming segment: check DPL against RPL and CPL. */
- if ( ((desc.b & (6u<<9)) != (6u<<9)) &&
- ((dpl < cpl) || (dpl < rpl)) )
- goto raise_exn;
- break;
- }
-
- /* Ensure Accessed flag is set. */
- new_desc_b = desc.b | a_flag;
- rc = ((desc.b & a_flag) ? X86EMUL_OKAY :
- ops->cmpxchg(
- x86_seg_none, desctab.base + (sel & 0xfff8) + 4,
- &desc.b, &new_desc_b, 4, ctxt));
- } while ( rc == X86EMUL_CMPXCHG_FAILED );
+ switch ( seg )
+ {
+ case x86_seg_cs:
+ /* Code segment? */
+ if ( !(desc.b & (1u<<11)) )
+ goto raise_exn;
+ /* Non-conforming segment: check DPL against RPL. */
+ if ( ((desc.b & (6u<<9)) != (6u<<9)) && (dpl != rpl) )
+ goto raise_exn;
+ break;
+ case x86_seg_ss:
+ /* Writable data segment? */
+ if ( (desc.b & (5u<<9)) != (1u<<9) )
+ goto raise_exn;
+ if ( (dpl != cpl) || (dpl != rpl) )
+ goto raise_exn;
+ break;
+ case x86_seg_ldtr:
+ /* LDT system segment? */
+ if ( (desc.b & (15u<<8)) != (2u<<8) )
+ goto raise_exn;
+ goto skip_accessed_flag;
+ case x86_seg_tr:
+ /* Available TSS system segment? */
+ if ( (desc.b & (15u<<8)) != (9u<<8) )
+ goto raise_exn;
+ a_flag = 0x200; /* busy flag */
+ break;
+ default:
+ /* Readable code or data segment? */
+ if ( (desc.b & (5u<<9)) == (4u<<9) )
+ goto raise_exn;
+ /* Non-conforming segment: check DPL against RPL and CPL. */
+ if ( ((desc.b & (6u<<9)) != (6u<<9)) &&
+ ((dpl < cpl) || (dpl < rpl)) )
+ goto raise_exn;
+ break;
+ }
- if ( rc )
+ /* Ensure Accessed flag is set. */
+ new_desc_b = desc.b | a_flag;
+ if ( !(desc.b & a_flag) &&
+ ((rc = ops->cmpxchg(
+ x86_seg_none, desctab.base + (sel & 0xfff8) + 4,
+ &desc.b, &new_desc_b, 4, ctxt)) != 0) )
return rc;
/* Force the Accessed flag in our local copy. */
