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KVM: x86 emulator: add syscall emulation 

Handle #UD intercept of the syscall instruction in 32bit compat mode on
an Intel host.
Setup the segment descriptors for CS and SS and the EIP/ESP registers
according to the manual. Save the RIP and EFLAGS to the correct registers.

[avi: fix build on i386 due to missing R11]

Signed-off-by: Christoph Egger <christoph.egger@amd.com>
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Andre Przywara 2009-06-18 12:56:00 +02:00 committed by Avi Kivity
parent e99f050712
commit e66bb2ccdc
1 changed files with 83 additions and 1 deletions
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84
arch/x86/kvm/x86_emulate.c
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@ -1397,6 +1397,85 @@ static void toggle_interruptibility(struct x86_emulate_ctxt *ctxt, u32 mask)
ctxt->interruptibility = mask;
}
static inline void
setup_syscalls_segments(struct x86_emulate_ctxt *ctxt,
struct kvm_segment *cs, struct kvm_segment *ss)
{
memset(cs, 0, sizeof(struct kvm_segment));
kvm_x86_ops->get_segment(ctxt->vcpu, cs, VCPU_SREG_CS);
memset(ss, 0, sizeof(struct kvm_segment));
cs->l = 0; /* will be adjusted later */
cs->base = 0; /* flat segment */
cs->g = 1; /* 4kb granularity */
cs->limit = 0xffffffff; /* 4GB limit */
cs->type = 0x0b; /* Read, Execute, Accessed */
cs->s = 1;
cs->dpl = 0; /* will be adjusted later */
cs->present = 1;
cs->db = 1;
ss->unusable = 0;
ss->base = 0; /* flat segment */
ss->limit = 0xffffffff; /* 4GB limit */
ss->g = 1; /* 4kb granularity */
ss->s = 1;
ss->type = 0x03; /* Read/Write, Accessed */
ss->db = 1; /* 32bit stack segment */
ss->dpl = 0;
ss->present = 1;
}
static int
emulate_syscall(struct x86_emulate_ctxt *ctxt)
{
struct decode_cache *c = &ctxt->decode;
struct kvm_segment cs, ss;
u64 msr_data;
/* syscall is not available in real mode */
if (c->lock_prefix || ctxt->mode == X86EMUL_MODE_REAL
|| !(ctxt->vcpu->arch.cr0 & X86_CR0_PE))
return -1;
setup_syscalls_segments(ctxt, &cs, &ss);
kvm_x86_ops->get_msr(ctxt->vcpu, MSR_STAR, &msr_data);
msr_data >>= 32;
cs.selector = (u16)(msr_data & 0xfffc);
ss.selector = (u16)(msr_data + 8);
if (is_long_mode(ctxt->vcpu)) {
cs.db = 0;
cs.l = 1;
}
kvm_x86_ops->set_segment(ctxt->vcpu, &cs, VCPU_SREG_CS);
kvm_x86_ops->set_segment(ctxt->vcpu, &ss, VCPU_SREG_SS);
c->regs[VCPU_REGS_RCX] = c->eip;
if (is_long_mode(ctxt->vcpu)) {
#ifdef CONFIG_X86_64
c->regs[VCPU_REGS_R11] = ctxt->eflags & ~EFLG_RF;
kvm_x86_ops->get_msr(ctxt->vcpu,
ctxt->mode == X86EMUL_MODE_PROT64 ?
MSR_LSTAR : MSR_CSTAR, &msr_data);
c->eip = msr_data;
kvm_x86_ops->get_msr(ctxt->vcpu, MSR_SYSCALL_MASK, &msr_data);
ctxt->eflags &= ~(msr_data | EFLG_RF);
#endif
} else {
/* legacy mode */
kvm_x86_ops->get_msr(ctxt->vcpu, MSR_STAR, &msr_data);
c->eip = (u32)msr_data;
ctxt->eflags &= ~(EFLG_VM | EFLG_IF | EFLG_RF);
}
return 0;
}
int
x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
{
@ -1993,7 +2072,10 @@ twobyte_insn:
}
break;
case 0x05: /* syscall */
goto cannot_emulate;
if (emulate_syscall(ctxt) == -1)
goto cannot_emulate;
else
goto writeback;
break;
case 0x06:
emulate_clts(ctxt->vcpu);