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Message-ID: <2e81cf29-65fd-74fc-db4f-95c453acc327@suse.com> Date: Fri, 4 Aug 2023 07:58:21 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.1 From: Jan Beulich Subject: [PATCH v3] x86emul: further correct 64-bit mode zero count repeated string insn handling To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: FR0P281CA0133.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:97::11) To DU2PR04MB8790.eurprd04.prod.outlook.com (2603:10a6:10:2e1::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DU2PR04MB8790:EE_|PAXPR04MB8302:EE_ X-MS-Office365-Filtering-Correlation-Id: 5e7e4dda-d52c-4a67-4aa5-08db94afd02d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DU2PR04MB8790.eurprd04.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230028)(346002)(39860400002)(396003)(366004)(376002)(136003)(451199021)(1800799003)(186006)(86362001)(478600001)(2616005)(54906003)(36756003)(6512007)(316002)(26005)(66946007)(66556008)(6916009)(66476007)(38100700002)(6486002)(4326008)(31696002)(6506007)(41300700001)(8936002)(8676002)(31686004)(83380400001)(5660300002)(2906002)(43740500002)(45980500001);DIR:OUT;SFP:1101; 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charset="utf-8" In an entirely different context I came across Linux commit 428e3d08574b ("KVM: x86: Fix zero iterations REP-string"), which points out that we're still doing things wrong: For one, there's no zero-extension at all on AMD. And then while RCX is zero-extended from 32 bits uniformly for all string instructions on newer hardware, RSI/RDI are only for MOVS and STOS on the systems I have access to. (On an old family 0xf system I've further found that for REP LODS even RCX is not zero-extended.) Fixes: 79e996a89f69 ("x86emul: correct 64-bit mode repeated string insn han= dling with zero count") Signed-off-by: Jan Beulich --- Partly RFC for none of this being documented anywhere (and it partly being model specific); inquiry pending. If I was asked, I would have claimed to have tested all string insns and for both vendors back at the time. But pretty clearly I didn't, and instead I did derive uniform behavior from just the MOVS and STOS observations on just Intel hardware; I'm sorry for that. --- v3: Re-base. v2: Re-base over re-ordering against previously 2nd patch in a series. --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -489,7 +489,7 @@ static inline void put_loop_count( regs->r(cx) =3D ad_bytes =3D=3D 4 ? (uint32_t)count : count; } =20 -#define get_rep_prefix(using_si, using_di) ({ \ +#define get_rep_prefix(extend_si, extend_di) ({ \ unsigned long max_reps =3D 1; \ if ( rep_prefix() ) \ max_reps =3D get_loop_count(&_regs, ad_bytes); \ @@ -497,14 +497,14 @@ static inline void put_loop_count( { \ /* \ * Skip the instruction if no repetitions are required, but \ - * zero extend involved registers first when using 32-bit \ + * zero extend relevant registers first when using 32-bit \ * addressing in 64-bit mode. \ */ \ - if ( mode_64bit() && ad_bytes =3D=3D 4 ) = \ + if ( !amd_like(ctxt) && mode_64bit() && ad_bytes =3D=3D 4 ) = \ { \ _regs.r(cx) =3D 0; \ - if ( using_si ) _regs.r(si) =3D (uint32_t)_regs.r(si); \ - if ( using_di ) _regs.r(di) =3D (uint32_t)_regs.r(di); \ + if ( extend_si ) _regs.r(si) =3D (uint32_t)_regs.r(si); \ + if ( extend_di ) _regs.r(di) =3D (uint32_t)_regs.r(di); \ } \ goto complete_insn; \ } \ @@ -1775,7 +1775,7 @@ x86_emulate( dst.bytes =3D !(b & 1) ? 1 : (op_bytes =3D=3D 8) ? 4 : op_bytes; if ( (rc =3D ioport_access_check(port, dst.bytes, ctxt, ops)) !=3D= 0 ) goto done; - nr_reps =3D get_rep_prefix(false, true); + nr_reps =3D get_rep_prefix(false, false); dst.mem.off =3D truncate_ea_and_reps(_regs.r(di), nr_reps, dst.byt= es); dst.mem.seg =3D x86_seg_es; /* Try the presumably most efficient approach first. */ @@ -1817,7 +1817,7 @@ x86_emulate( dst.bytes =3D !(b & 1) ? 1 : (op_bytes =3D=3D 8) ? 4 : op_bytes; if ( (rc =3D ioport_access_check(port, dst.bytes, ctxt, ops)) !=3D= 0 ) goto done; - nr_reps =3D get_rep_prefix(true, false); + nr_reps =3D get_rep_prefix(false, false); ea.mem.off =3D truncate_ea_and_reps(_regs.r(si), nr_reps, dst.byte= s); /* Try the presumably most efficient approach first. */ if ( !ops->rep_outs ) @@ -2154,7 +2154,7 @@ x86_emulate( case 0xa6 ... 0xa7: /* cmps */ { unsigned long next_eip =3D _regs.r(ip); =20 - get_rep_prefix(true, true); + get_rep_prefix(false, false); src.bytes =3D dst.bytes =3D (d & ByteOp) ? 1 : op_bytes; if ( (rc =3D read_ulong(ea.mem.seg, truncate_ea(_regs.r(si)), &dst.val, dst.bytes, ctxt, ops)) || @@ -2196,7 +2196,7 @@ x86_emulate( } =20 case 0xac ... 0xad: /* lods */ - get_rep_prefix(true, false); + get_rep_prefix(false, false); if ( (rc =3D read_ulong(ea.mem.seg, truncate_ea(_regs.r(si)), &dst.val, dst.bytes, ctxt, ops)) !=3D 0 ) goto done; @@ -2207,7 +2207,7 @@ x86_emulate( case 0xae ... 0xaf: /* scas */ { unsigned long next_eip =3D _regs.r(ip); =20 - get_rep_prefix(false, true); + get_rep_prefix(false, false); if ( (rc =3D read_ulong(x86_seg_es, truncate_ea(_regs.r(di)), &dst.val, src.bytes, ctxt, ops)) !=3D 0 ) goto done;