ia64/xen-unstable

changeset 4499:f301b12bedde

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bitkeeper revision 1.1283 (4254ed0bK7tEfc4Z935RO2wbK5HcPw)

Properly ensure that every write to GS is followed by a serialising
instruction before the next SWAPGS (AMD erratum #88). We only resort
to adding an otherwise unnecessary mfence in two cases.
Signed-off-by: Keir Fraser <keir@xensource.com>
author kaf24@firebug.cl.cam.ac.uk
date Thu Apr 07 08:19:23 2005 +0000 (2005-04-07)
parents 3f2415a328b7
children 608f95d3df77
files xen/arch/x86/domain.c
line diff
     1.1 --- a/xen/arch/x86/domain.c	Thu Apr 07 08:01:29 2005 +0000
     1.2 +++ b/xen/arch/x86/domain.c	Thu Apr 07 08:19:23 2005 +0000
     1.3 @@ -585,22 +585,21 @@ static void load_segments(struct exec_do
     1.4                n->arch.user_ctxt.fs_base,
     1.5                n->arch.user_ctxt.fs_base>>32);
     1.6  
     1.7 +    /* Most kernels have non-zero GS base, so don't bother testing. */
     1.8 +    /* (This is also a serialising instruction, avoiding AMD erratum #88.) */
     1.9 +    wrmsr(MSR_SHADOW_GS_BASE,
    1.10 +          n->arch.user_ctxt.gs_base_kernel,
    1.11 +          n->arch.user_ctxt.gs_base_kernel>>32);
    1.12 +
    1.13      /* This can only be non-zero if selector is NULL. */
    1.14      if ( n->arch.user_ctxt.gs_base_user )
    1.15          wrmsr(MSR_GS_BASE,
    1.16                n->arch.user_ctxt.gs_base_user,
    1.17                n->arch.user_ctxt.gs_base_user>>32);
    1.18  
    1.19 -    /* This can only be non-zero if selector is NULL. */
    1.20 -    if ( p->arch.user_ctxt.gs_base_kernel |
    1.21 -         n->arch.user_ctxt.gs_base_kernel )
    1.22 -        wrmsr(MSR_SHADOW_GS_BASE,
    1.23 -              n->arch.user_ctxt.gs_base_kernel,
    1.24 -              n->arch.user_ctxt.gs_base_kernel>>32);
    1.25 -
    1.26      /* If in kernel mode then switch the GS bases around. */
    1.27      if ( n->arch.flags & TF_kernel_mode )
    1.28 -        __asm__ __volatile__ ( safe_swapgs );
    1.29 +        __asm__ __volatile__ ( "swapgs" );
    1.30  
    1.31      if ( unlikely(!all_segs_okay) )
    1.32      {