Re: [PATCH RFC 4/5] x86: KVM: add xsetbv to the emulator

Vitaly Kuznetsov
2019-07-31T13:07:29Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 20/06/19 13:02, Vitaly Kuznetsov wrote:
>> To avoid hardcoding xsetbv length to '3' we need to support decoding it in
>> the emulator.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>
> Can you also emulate it properly? The code from QEMU's
> target/i386/fpu_helper.c can help. :)
>

(Had a chance to get back to this just now, sorry)

Assuming __kvm_set_xcr() is also a correct implementation, would the
code below do the job? (Just trying to figure out why you suggested
me to take a look at QEMU's variant):

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index feab24cac610..77cf6c11f66b 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -229,7 +229,7 @@ struct x86_emulate_ops {
int (*pre_leave_smm)(struct x86_emulate_ctxt *ctxt,
const char *smstate);
void (*post_leave_smm)(struct x86_emulate_ctxt *ctxt);
-
+ int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr);
};

typedef u32 __attribute__((vector_size(16))) sse128_t;
@@ -429,6 +429,7 @@ enum x86_intercept {
x86_intercept_ins,
x86_intercept_out,
x86_intercept_outs,
+ x86_intercept_xsetbv,

nr_x86_intercepts
};
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 718f7d9afedc..f9e843dd992a 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4156,6 +4156,20 @@ static int em_fxrstor(struct x86_emulate_ctxt *ctxt)
return rc;
}

+static int em_xsetbv(struct x86_emulate_ctxt *ctxt)
+{
+ u32 eax, ecx, edx;
+
+ eax = reg_read(ctxt, VCPU_REGS_RAX);
+ edx = reg_read(ctxt, VCPU_REGS_RDX);
+ ecx = reg_read(ctxt, VCPU_REGS_RCX);
+
+ if (ctxt->ops->set_xcr(ctxt, ecx, ((u64)edx << 32) | eax))
+ return emulate_gp(ctxt, 0);
+
+ return X86EMUL_CONTINUE;
+}
+
static bool valid_cr(int nr)
{
switch (nr) {
@@ -4409,6 +4423,12 @@ static const struct opcode group7_rm1[] = {
N, N, N, N, N, N,
};

+static const struct opcode group7_rm2[] = {
+ N,
+ II(ImplicitOps | Priv, em_xsetbv, xsetbv),
+ N, N, N, N, N, N,
+};
+
static const struct opcode group7_rm3[] = {
DIP(SrcNone | Prot | Priv, vmrun, check_svme_pa),
II(SrcNone | Prot | EmulateOnUD, em_hypercall, vmmcall),
@@ -4498,7 +4518,8 @@ static const struct group_dual group7 = { {
}, {
EXT(0, group7_rm0),
EXT(0, group7_rm1),
- N, EXT(0, group7_rm3),
+ EXT(0, group7_rm2),
+ EXT(0, group7_rm3),
II(SrcNone | DstMem | Mov, em_smsw, smsw), N,
II(SrcMem16 | Mov | Priv, em_lmsw, lmsw),
EXT(0, group7_rm7),
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c6d951cbd76c..9512cc38dfe9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6068,6 +6068,11 @@ static void emulator_post_leave_smm(struct x86_emulate_ctxt *ctxt)
kvm_smm_changed(emul_to_vcpu(ctxt));
}

+static int emulator_set_xcr(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr)
+{
+ return __kvm_set_xcr(emul_to_vcpu(ctxt), index, xcr);
+}
+
static const struct x86_emulate_ops emulate_ops = {
.read_gpr = emulator_read_gpr,
.write_gpr = emulator_write_gpr,
@@ -6109,6 +6114,7 @@ static const struct x86_emulate_ops emulate_ops = {
.set_hflags = emulator_set_hflags,
.pre_leave_smm = emulator_pre_leave_smm,
.post_leave_smm = emulator_post_leave_smm,
+ .set_xcr = emulator_set_xcr,
};

static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)

--
Vitaly