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Re: [RFC v1 3/7] x86/emul: Separate out instruction completion
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 19 May 2026 12:08:15 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 19 May 2026 10:08:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18.05.2026 15:14, Ross Lagerwall wrote:
> To support merging the emulated instruction and VMEXIT paths, split out
> instruction completion from the core x86 emulation so it can be called
> separately.
You don't mean to use a full-fledged struct x86_emulate_ctxt on the VMEXIT
paths, do you?
> @@ -1265,8 +1281,6 @@ x86_emulate(
> uint8_t b, d, *opc = NULL;
> unsigned int first_byte = 0, elem_bytes, insn_bytes = 0;
> uint64_t op_mask = ~0ULL;
> - bool singlestep = (_regs.eflags & X86_EFLAGS_TF) &&
> - !is_branch_step(ctxt, ops);
Nit: Yes, indentation was screwed here. Please ...
> @@ -1280,6 +1294,9 @@ x86_emulate(
>
> init_context(ctxt);
>
> + ctxt->singlestep = (_regs.eflags & X86_EFLAGS_TF) &&
> + !is_branch_step(ctxt, ops);
... correct such when moving code around.
> @@ -8347,17 +8364,6 @@ x86_emulate(
> put_fpu(fpu_type, false, state, ctxt, ops);
> fpu_type = X86EMUL_FPU_none;
>
> - /* Zero the upper 32 bits of %rip if not in 64-bit mode. */
> - if ( !mode_64bit() )
> - _regs.r(ip) = (uint32_t)_regs.r(ip);
While, because you have the new helper update ctxt->regs, the removal of
this update of _regs looks technically okay, ...
> - /* Should a singlestep #DB be raised? */
> - if ( rc == X86EMUL_OKAY && singlestep && !ctxt->retire.mov_ss )
> - {
> - ctxt->retire.singlestep = true;
> - ctxt->retire.sti = false;
> - }
> -
> if ( rc != X86EMUL_DONE )
> *ctxt->regs = _regs;
... further uses of _regs here (not this one, but in general) would be at
risk of no longer working as expected (yet only in a corner case, so
possibly not covered by testing).
Jan
|
