The SDM says that exiting system management mode from 64-bit mode
is invalid, but that would be too good to be true. But actually,
most of the code is already there to support exiting from compat
mode (EFER.LME=1, EFER.LMA=0). Getting all the way from 64-bit
mode to real mode only requires clearing CS.L and CR4.PCIDE.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 660a5d517aaab9187f93854425c4c63f4a09195c
Cc: Laszlo Ersek <lersek@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/emulate.c | 30 +++++++++++++++++++++++++-----
1 file changed, 25 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b60fed56671b..1505587d06e9 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2484,16 +2484,36 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt)
/*
* Get back to real mode, to prepare a safe state in which to load
- * CR0/CR3/CR4/EFER.
- *
- * CR4.PCIDE must be zero, because it is a 64-bit mode only feature.
+ * CR0/CR3/CR4/EFER. It's all a bit more complicated if the vCPU
+ * supports long mode.
*/
+ cr4 = ctxt->ops->get_cr(ctxt, 4);
+ if (emulator_has_longmode(ctxt)) {
+ struct desc_struct cs_desc;
+
+ /* Zero CR4.PCIDE before CR0.PG. */
+ if (cr4 & X86_CR4_PCIDE) {
+ ctxt->ops->set_cr(ctxt, 4, cr4 & ~X86_CR4_PCIDE);
+ cr4 &= ~X86_CR4_PCIDE;
+ }
+
+ /* A 32-bit code segment is required to clear EFER.LMA. */
+ memset(&cs_desc, 0, sizeof(cs_desc));
+ cs_desc.type = 0xb;
+ cs_desc.s = cs_desc.g = cs_desc.p = 1;
+ ctxt->ops->set_segment(ctxt, 0, &cs_desc, 0, VCPU_SREG_CS);
+ }
+
+ /* For the 64-bit case, this will clear EFER.LMA. */
cr0 = ctxt->ops->get_cr(ctxt, 0);
if (cr0 & X86_CR0_PE)
ctxt->ops->set_cr(ctxt, 0, cr0 & ~(X86_CR0_PG | X86_CR0_PE));
- cr4 = ctxt->ops->get_cr(ctxt, 4);
+
+ /* Now clear CR4.PAE (which must be done before clearing EFER.LME). */
if (cr4 & X86_CR4_PAE)
ctxt->ops->set_cr(ctxt, 4, cr4 & ~X86_CR4_PAE);
+
+ /* And finally go back to 32-bit mode. */
efer = 0;
ctxt->ops->set_msr(ctxt, MSR_EFER, efer);
@@ -4454,7 +4474,7 @@ static const struct opcode twobyte_table[256] = {
F(DstMem | SrcReg | Src2CL | ModRM, em_shld), N, N,
/* 0xA8 - 0xAF */
I(Stack | Src2GS, em_push_sreg), I(Stack | Src2GS, em_pop_sreg),
- II(No64 | EmulateOnUD | ImplicitOps, em_rsm, rsm),
+ II(EmulateOnUD | ImplicitOps, em_rsm, rsm),
F(DstMem | SrcReg | ModRM | BitOp | Lock | PageTable, em_bts),
F(DstMem | SrcReg | Src2ImmByte | ModRM, em_shrd),
F(DstMem | SrcReg | Src2CL | ModRM, em_shrd),
--
1.8.3.1
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