ia64/xen-unstable

changeset 18342:504e5334f1a2

x86 hvm: Add clarifying comments about clipping repeated string
instructions to 4096 iterations.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Aug 19 18:52:04 2008 +0100 (2008-08-19)
parents e6a4f6a682ba
children a864ba2f0aa5
files xen/arch/x86/hvm/emulate.c
line diff
     1.1 --- a/xen/arch/x86/hvm/emulate.c	Tue Aug 19 18:47:01 2008 +0100
     1.2 +++ b/xen/arch/x86/hvm/emulate.c	Tue Aug 19 18:52:04 2008 +0100
     1.3 @@ -210,7 +210,10 @@ static int hvmemul_linear_to_phys(
     1.4      unsigned long pfn, npfn, done, todo, i;
     1.5      int reverse;
     1.6  
     1.7 -    /* Clip repetitions to a sensible maximum. */
     1.8 +    /*
     1.9 +     * Clip repetitions to a sensible maximum. This avoids extensive looping in
    1.10 +     * this function while still amortising the cost of I/O trap-and-emulate.
    1.11 +     */
    1.12      *reps = min_t(unsigned long, *reps, 4096);
    1.13  
    1.14      /* With no paging it's easy: linear == physical. */
    1.15 @@ -297,7 +300,13 @@ static int hvmemul_virtual_to_linear(
    1.16          return X86EMUL_OKAY;
    1.17      }
    1.18  
    1.19 +    /*
    1.20 +     * Clip repetitions to avoid overflow when multiplying by @bytes_per_rep.
    1.21 +     * The chosen maximum is very conservative but it's what we use in
    1.22 +     * hvmemul_linear_to_phys() so there is no point in using a larger value.
    1.23 +     */
    1.24      *reps = min_t(unsigned long, *reps, 4096);
    1.25 +
    1.26      reg = hvmemul_get_seg_reg(seg, hvmemul_ctxt);
    1.27  
    1.28      if ( (hvmemul_ctxt->ctxt.regs->eflags & X86_EFLAGS_DF) && (*reps > 1) )