From f41c88a6fca59f99a2eb5e7ed3d90ab7bca08b1b Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Thu, 30 Mar 2023 13:07:16 +0200 Subject: [PATCH] x86emul: pull permission check ahead for REP INS/OUTS Based on observations on a fair range of hardware from both primary vendors even zero-iteration-count instances of these insns perform the port related permission checking first. Fixes: fe300600464c ("x86: Fix emulation of REP prefix") Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- xen/arch/x86/x86_emulate/x86_emulate.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index e38f98b547..94dd72585a 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -4249,14 +4249,15 @@ x86_emulate( goto imul; case 0x6c ... 0x6d: /* ins %dx,%es:%edi */ { - unsigned long nr_reps = get_rep_prefix(false, true); + unsigned long nr_reps; unsigned int port = _regs.dx; dst.bytes = !(b & 1) ? 1 : (op_bytes == 8) ? 4 : op_bytes; - dst.mem.seg = x86_seg_es; - dst.mem.off = truncate_ea_and_reps(_regs.r(di), nr_reps, dst.bytes); if ( (rc = ioport_access_check(port, dst.bytes, ctxt, ops)) != 0 ) goto done; + nr_reps = get_rep_prefix(false, true); + dst.mem.off = truncate_ea_and_reps(_regs.r(di), nr_reps, dst.bytes); + dst.mem.seg = x86_seg_es; /* Try the presumably most efficient approach first. */ if ( !ops->rep_ins ) nr_reps = 1; @@ -4290,13 +4291,14 @@ x86_emulate( } case 0x6e ... 0x6f: /* outs %esi,%dx */ { - unsigned long nr_reps = get_rep_prefix(true, false); + unsigned long nr_reps; unsigned int port = _regs.dx; dst.bytes = !(b & 1) ? 1 : (op_bytes == 8) ? 4 : op_bytes; - ea.mem.off = truncate_ea_and_reps(_regs.r(si), nr_reps, dst.bytes); if ( (rc = ioport_access_check(port, dst.bytes, ctxt, ops)) != 0 ) goto done; + nr_reps = get_rep_prefix(true, false); + ea.mem.off = truncate_ea_and_reps(_regs.r(si), nr_reps, dst.bytes); /* Try the presumably most efficient approach first. */ if ( !ops->rep_outs ) nr_reps = 1; -- 2.39.5