On 12.03.2026 12:21, Alejandro Vallejo wrote:
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -3837,35 +3837,34 @@ void hvm_ud_intercept(struct cpu_user_regs *regs)
> struct vcpu *cur = current;
> bool should_emulate = false;
> struct hvm_emulate_ctxt ctxt;
> + const struct segment_register *cs;
> + uint32_t walk;
> + unsigned long addr;
> + char sig[5]; /* ud2; .ascii "xen" */
>
> hvm_emulate_init_once(&ctxt, NULL, regs);
>
> - if ( opt_hvm_fep )
> + cs = &ctxt.seg_reg[x86_seg_cs];
> + walk = ((ctxt.seg_reg[x86_seg_ss].dpl == 3)
> + ? PFEC_user_mode : 0) | PFEC_insn_fetch;
While of course functionally everything's fine this way, I'm now entirely lost:
Why are what were ...
> + if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->rip,
> + sizeof(sig), hvm_access_insn_fetch,
> + cs, &addr) &&
> + (hvm_copy_from_guest_linear(sig, addr, sizeof(sig),
> + walk, NULL) == HVMTRANS_okay) &&
> + (memcmp(sig, "\xf\xb" "xen", sizeof(sig)) == 0) )
> {
> - const struct segment_register *cs = &ctxt.seg_reg[x86_seg_cs];
> - uint32_t walk = ((ctxt.seg_reg[x86_seg_ss].dpl == 3)
> - ? PFEC_user_mode : 0) | PFEC_insn_fetch;
... initializers before not initializers anymore, when all you're doing is
(supposedly) re-indentation (and, necessarily, moving decls up to the top of
the scope they need to live in)?
> - unsigned long addr;
> - char sig[5]; /* ud2; .ascii "xen" */
> -
> - if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->rip,
> - sizeof(sig), hvm_access_insn_fetch,
> - cs, &addr) &&
> - (hvm_copy_from_guest_linear(sig, addr, sizeof(sig),
> - walk, NULL) == HVMTRANS_okay) &&
> - (memcmp(sig, "\xf\xb" "xen", sizeof(sig)) == 0) )
> - {
> - regs->rip += sizeof(sig);
> - regs->eflags &= ~X86_EFLAGS_RF;
> + regs->rip += sizeof(sig);
> + regs->eflags &= ~X86_EFLAGS_RF;
>
> - /* Zero the upper 32 bits of %rip if not in 64bit mode. */
> - if ( !(hvm_long_mode_active(cur) && cs->l) )
> - regs->rip = (uint32_t)regs->rip;
> + /* Zero the upper 32 bits of %rip if not in 64bit mode. */
> + if ( !(hvm_long_mode_active(cur) && cs->l) )
> + regs->rip = (uint32_t)regs->rip;
>
> - add_taint(TAINT_HVM_FEP);
> + add_taint(TAINT_HVM_FEP);
>
> - should_emulate = true;
> - }
> + should_emulate = true;
> }
>
> if ( !should_emulate )
With this, the purpose of the should_emulate variable effectively vanishes,
without it actually being purged (unlike you had it earlier).
Jan
