From 939a9e800c4156677c10c6cf08fde071e9b86eaf Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Thu, 14 Nov 2024 13:03:18 +0100 Subject: [PATCH] x86emul: avoid double memory read for RORX Originally only twobyte_table[0x3a] determined what part of generic operand fetching (near the top of x86_emulate()) comes into play. When ext0f3a_table[] was added, ->desc was updated to properly describe the ModR/M byte's function. With that generic source operand fetching came into play for RORX, rendering the explicit fetching in the respective case block redundant (and wrong at the very least when MMIO with side effects is accessed). While there also make a purely cosmetic / documentary adjustment to ext0f3a_table[]: RORX really is a 2-operand insn, MOV-like in that it only writes its destination register. Fixes: 9f7f5f6bc95b ("x86emul: add tables for 0f38 and 0f3a extension space") Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- xen/arch/x86/x86_emulate/decode.c | 2 +- xen/arch/x86/x86_emulate/x86_emulate.c | 5 ----- 2 files changed, 1 insertion(+), 6 deletions(-) diff --git a/xen/arch/x86/x86_emulate/decode.c b/xen/arch/x86/x86_emulate/decode.c index 0a0751f2ed..7ce97c4726 100644 --- a/xen/arch/x86/x86_emulate/decode.c +++ b/xen/arch/x86/x86_emulate/decode.c @@ -521,7 +521,7 @@ static const struct ext0f3a_table { [0xce ... 0xcf] = { .simd_size = simd_packed_int, .d8s = d8s_vl }, [0xde] = { .simd_size = simd_other }, [0xdf] = { .simd_size = simd_packed_int, .two_op = 1 }, - [0xf0] = {}, + [0xf0] = { .two_op = 1 /* Mov */ }, }; static const opcode_desc_t xop_table[] = { diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index c91d048d26..0600df789c 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -7699,11 +7699,6 @@ x86_emulate( case X86EMUL_OPC_VEX_F2(0x0f3a, 0xf0): /* rorx imm,r/m,r */ vcpu_must_have(bmi2); generate_exception_if(vex.l || vex.reg != 0xf, X86_EXC_UD); - if ( ea.type == OP_REG ) - src.val = *ea.reg; - else if ( (rc = read_ulong(ea.mem.seg, ea.mem.off, &src.val, op_bytes, - ctxt, ops)) != X86EMUL_OKAY ) - goto done; if ( mode_64bit() && vex.w ) asm ( "rorq %b1,%0" : "=g" (dst.val) : "c" (imm1), "0" (src.val) ); else