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KVM: emulate: protect checks on ctxt->d by a common "if (unlikely())"
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There are several checks for "peculiar" aspects of instructions in both
x86_decode_insn and x86_emulate_insn.  Group them together, and guard
them with a single "if" that lets the processor quickly skip them all.
Make this more effective by adding two more flag bits that say whether the
.intercept and .check_perm fields are valid.  We will reuse these
flags later to avoid initializing fields of the emulate_ctxt struct.

This skims about 30 cycles for each emulated instructions, which is
approximately a 3% improvement.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Paolo Bonzini committed Jul 11, 2014
1 parent e24186e commit d40a689
Showing 1 changed file with 94 additions and 81 deletions.
175 changes: 94 additions & 81 deletions arch/x86/kvm/emulate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,8 @@
#define NoWrite ((u64)1 << 45) /* No writeback */
#define SrcWrite ((u64)1 << 46) /* Write back src operand */
#define NoMod ((u64)1 << 47) /* Mod field is ignored */
#define Intercept ((u64)1 << 48) /* Has valid intercept field */
#define CheckPerm ((u64)1 << 49) /* Has valid check_perm field */

#define DstXacc (DstAccLo | SrcAccHi | SrcWrite)

Expand Down Expand Up @@ -3546,9 +3548,9 @@ static int check_perm_out(struct x86_emulate_ctxt *ctxt)
}

#define D(_y) { .flags = (_y) }
#define DI(_y, _i) { .flags = (_y), .intercept = x86_intercept_##_i }
#define DIP(_y, _i, _p) { .flags = (_y), .intercept = x86_intercept_##_i, \
.check_perm = (_p) }
#define DI(_y, _i) { .flags = (_y)|Intercept, .intercept = x86_intercept_##_i }
#define DIP(_y, _i, _p) { .flags = (_y)|Intercept|CheckPerm, \
.intercept = x86_intercept_##_i, .check_perm = (_p) }
#define N D(NotImpl)
#define EXT(_f, _e) { .flags = ((_f) | RMExt), .u.group = (_e) }
#define G(_f, _g) { .flags = ((_f) | Group | ModRM), .u.group = (_g) }
Expand All @@ -3557,10 +3559,10 @@ static int check_perm_out(struct x86_emulate_ctxt *ctxt)
#define I(_f, _e) { .flags = (_f), .u.execute = (_e) }
#define F(_f, _e) { .flags = (_f) | Fastop, .u.fastop = (_e) }
#define II(_f, _e, _i) \
{ .flags = (_f), .u.execute = (_e), .intercept = x86_intercept_##_i }
{ .flags = (_f)|Intercept, .u.execute = (_e), .intercept = x86_intercept_##_i }
#define IIP(_f, _e, _i, _p) \
{ .flags = (_f), .u.execute = (_e), .intercept = x86_intercept_##_i, \
.check_perm = (_p) }
{ .flags = (_f)|Intercept|CheckPerm, .u.execute = (_e), \
.intercept = x86_intercept_##_i, .check_perm = (_p) }
#define GP(_f, _g) { .flags = ((_f) | Prefix), .u.gprefix = (_g) }

#define D2bv(_f) D((_f) | ByteOp), D(_f)
Expand Down Expand Up @@ -4393,29 +4395,37 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
return EMULATION_FAILED;

ctxt->execute = opcode.u.execute;
ctxt->check_perm = opcode.check_perm;
ctxt->intercept = opcode.intercept;

if (ctxt->d & NotImpl)
return EMULATION_FAILED;
if (unlikely(ctxt->d &
(NotImpl|EmulateOnUD|Stack|Op3264|Sse|Mmx|Intercept|CheckPerm))) {
/*
* These are copied unconditionally here, and checked unconditionally
* in x86_emulate_insn.
*/
ctxt->check_perm = opcode.check_perm;
ctxt->intercept = opcode.intercept;

if (!(ctxt->d & EmulateOnUD) && ctxt->ud)
return EMULATION_FAILED;
if (ctxt->d & NotImpl)
return EMULATION_FAILED;

if (mode == X86EMUL_MODE_PROT64 && (ctxt->d & Stack))
ctxt->op_bytes = 8;
if (!(ctxt->d & EmulateOnUD) && ctxt->ud)
return EMULATION_FAILED;

if (ctxt->d & Op3264) {
if (mode == X86EMUL_MODE_PROT64)
if (mode == X86EMUL_MODE_PROT64 && (ctxt->d & Stack))
ctxt->op_bytes = 8;
else
ctxt->op_bytes = 4;
}

if (ctxt->d & Sse)
ctxt->op_bytes = 16;
else if (ctxt->d & Mmx)
ctxt->op_bytes = 8;
if (ctxt->d & Op3264) {
if (mode == X86EMUL_MODE_PROT64)
ctxt->op_bytes = 8;
else
ctxt->op_bytes = 4;
}

if (ctxt->d & Sse)
ctxt->op_bytes = 16;
else if (ctxt->d & Mmx)
ctxt->op_bytes = 8;
}

/* ModRM and SIB bytes. */
if (ctxt->d & ModRM) {
Expand Down Expand Up @@ -4549,75 +4559,78 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
goto done;
}

if ((ctxt->mode == X86EMUL_MODE_PROT64 && (ctxt->d & No64)) ||
(ctxt->d & Undefined)) {
rc = emulate_ud(ctxt);
goto done;
}

if (((ctxt->d & (Sse|Mmx)) && ((ops->get_cr(ctxt, 0) & X86_CR0_EM)))
|| ((ctxt->d & Sse) && !(ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR))) {
rc = emulate_ud(ctxt);
goto done;
}

if ((ctxt->d & (Sse|Mmx)) && (ops->get_cr(ctxt, 0) & X86_CR0_TS)) {
rc = emulate_nm(ctxt);
goto done;
}
if (unlikely(ctxt->d &
(No64|Undefined|Sse|Mmx|Intercept|CheckPerm|Priv|Prot|String))) {
if ((ctxt->mode == X86EMUL_MODE_PROT64 && (ctxt->d & No64)) ||
(ctxt->d & Undefined)) {
rc = emulate_ud(ctxt);
goto done;
}

if (ctxt->d & Mmx) {
rc = flush_pending_x87_faults(ctxt);
if (rc != X86EMUL_CONTINUE)
if (((ctxt->d & (Sse|Mmx)) && ((ops->get_cr(ctxt, 0) & X86_CR0_EM)))
|| ((ctxt->d & Sse) && !(ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR))) {
rc = emulate_ud(ctxt);
goto done;
/*
* Now that we know the fpu is exception safe, we can fetch
* operands from it.
*/
fetch_possible_mmx_operand(ctxt, &ctxt->src);
fetch_possible_mmx_operand(ctxt, &ctxt->src2);
if (!(ctxt->d & Mov))
fetch_possible_mmx_operand(ctxt, &ctxt->dst);
}
}

if (unlikely(ctxt->guest_mode) && ctxt->intercept) {
rc = emulator_check_intercept(ctxt, ctxt->intercept,
X86_ICPT_PRE_EXCEPT);
if (rc != X86EMUL_CONTINUE)
if ((ctxt->d & (Sse|Mmx)) && (ops->get_cr(ctxt, 0) & X86_CR0_TS)) {
rc = emulate_nm(ctxt);
goto done;
}
}

/* Privileged instruction can be executed only in CPL=0 */
if ((ctxt->d & Priv) && ops->cpl(ctxt)) {
rc = emulate_gp(ctxt, 0);
goto done;
}
if (ctxt->d & Mmx) {
rc = flush_pending_x87_faults(ctxt);
if (rc != X86EMUL_CONTINUE)
goto done;
/*
* Now that we know the fpu is exception safe, we can fetch
* operands from it.
*/
fetch_possible_mmx_operand(ctxt, &ctxt->src);
fetch_possible_mmx_operand(ctxt, &ctxt->src2);
if (!(ctxt->d & Mov))
fetch_possible_mmx_operand(ctxt, &ctxt->dst);
}

/* Instruction can only be executed in protected mode */
if ((ctxt->d & Prot) && ctxt->mode < X86EMUL_MODE_PROT16) {
rc = emulate_ud(ctxt);
goto done;
}
if (unlikely(ctxt->guest_mode) && ctxt->intercept) {
rc = emulator_check_intercept(ctxt, ctxt->intercept,
X86_ICPT_PRE_EXCEPT);
if (rc != X86EMUL_CONTINUE)
goto done;
}

/* Do instruction specific permission checks */
if (ctxt->check_perm) {
rc = ctxt->check_perm(ctxt);
if (rc != X86EMUL_CONTINUE)
/* Privileged instruction can be executed only in CPL=0 */
if ((ctxt->d & Priv) && ops->cpl(ctxt)) {
rc = emulate_gp(ctxt, 0);
goto done;
}
}

if (unlikely(ctxt->guest_mode) && ctxt->intercept) {
rc = emulator_check_intercept(ctxt, ctxt->intercept,
X86_ICPT_POST_EXCEPT);
if (rc != X86EMUL_CONTINUE)
/* Instruction can only be executed in protected mode */
if ((ctxt->d & Prot) && ctxt->mode < X86EMUL_MODE_PROT16) {
rc = emulate_ud(ctxt);
goto done;
}
}

if (ctxt->rep_prefix && (ctxt->d & String)) {
/* All REP prefixes have the same first termination condition */
if (address_mask(ctxt, reg_read(ctxt, VCPU_REGS_RCX)) == 0) {
ctxt->eip = ctxt->_eip;
goto done;
/* Do instruction specific permission checks */
if (ctxt->check_perm) {
rc = ctxt->check_perm(ctxt);
if (rc != X86EMUL_CONTINUE)
goto done;
}

if (unlikely(ctxt->guest_mode) && ctxt->intercept) {
rc = emulator_check_intercept(ctxt, ctxt->intercept,
X86_ICPT_POST_EXCEPT);
if (rc != X86EMUL_CONTINUE)
goto done;
}

if (ctxt->rep_prefix && (ctxt->d & String)) {
/* All REP prefixes have the same first termination condition */
if (address_mask(ctxt, reg_read(ctxt, VCPU_REGS_RCX)) == 0) {
ctxt->eip = ctxt->_eip;
goto done;
}
}
}

Expand Down

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