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Subject[PATCH] KVM: X86: avoid unused setup_syscalls_segments call when SYSCALL check failed
Date
From: Miaohe Lin <linmiaohe@huawei.com>

When SYSCALL/SYSENTER ability check failed, cs and ss is inited but
remain not used. Delay initializing cs and ss until SYSCALL/SYSENTER
ability check passed.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
arch/x86/kvm/emulate.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 698efb8c3897..952d1a4f4d7e 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2770,11 +2770,10 @@ static int em_syscall(struct x86_emulate_ctxt *ctxt)
return emulate_ud(ctxt);

ops->get_msr(ctxt, MSR_EFER, &efer);
- setup_syscalls_segments(ctxt, &cs, &ss);
-
if (!(efer & EFER_SCE))
return emulate_ud(ctxt);

+ setup_syscalls_segments(ctxt, &cs, &ss);
ops->get_msr(ctxt, MSR_STAR, &msr_data);
msr_data >>= 32;
cs_sel = (u16)(msr_data & 0xfffc);
@@ -2838,12 +2837,11 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
if (ctxt->mode == X86EMUL_MODE_PROT64)
return X86EMUL_UNHANDLEABLE;

- setup_syscalls_segments(ctxt, &cs, &ss);
-
ops->get_msr(ctxt, MSR_IA32_SYSENTER_CS, &msr_data);
if ((msr_data & 0xfffc) == 0x0)
return emulate_gp(ctxt, 0);

+ setup_syscalls_segments(ctxt, &cs, &ss);
ctxt->eflags &= ~(X86_EFLAGS_VM | X86_EFLAGS_IF);
cs_sel = (u16)msr_data & ~SEGMENT_RPL_MASK;
ss_sel = cs_sel + 8;
--
2.19.1
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