lkml.org 
[lkml]   [2020]   [Mar]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] KVM: X86: Avoid explictly fetch instruction in x86_decode_insn()
Date
Hi:
Peter Xu <peterx@redhat.com> writes:
>insn_fetch() will always implicitly refill instruction buffer properly when the buffer is empty, so we don't need to explicitly fetch it even if insn_len==0 for x86_decode_insn().
>
>Signed-off-by: Peter Xu <peterx@redhat.com>
>---
> arch/x86/kvm/emulate.c | 5 -----
> 1 file changed, 5 deletions(-)
>
>diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index dd19fb3539e0..04f33c1ca926 100644
>--- a/arch/x86/kvm/emulate.c
>+++ b/arch/x86/kvm/emulate.c
>@@ -5175,11 +5175,6 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
> ctxt->opcode_len = 1;
> if (insn_len > 0)
> memcpy(ctxt->fetch.data, insn, insn_len);
>- else {
>- rc = __do_insn_fetch_bytes(ctxt, 1);
>- if (rc != X86EMUL_CONTINUE)
>- goto done;
>- }
>
> switch (mode) {
> case X86EMUL_MODE_REAL:

Looks good, thanks. But it seems we should also take care of the comment in __do_insn_fetch_bytes(), as we do not
load instruction at the beginning of x86_decode_insn() now, which may be misleading:
/*
* One instruction can only straddle two pages,
* and one has been loaded at the beginning of
* x86_decode_insn. So, if not enough bytes
* still, we must have hit the 15-byte boundary.
*/
if (unlikely(size < op_size))
return emulate_gp(ctxt, 0);

\
 
 \ /
  Last update: 2020-03-04 03:39    [W:0.129 / U:0.328 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site