On 11/03/15 14:46, Paolo Bonzini wrote:
>
>
> On 03/11/2015 14:40, Laszlo Ersek wrote:
>> On 11/03/15 14:29, Paolo Bonzini wrote:
>>> 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: sta...@vger.kernel.org
>>> Fixes: 660a5d517aaab9187f93854425c4c63f4a09195c
>>> Cc: Laszlo Ersek <ler...@redhat.com>
>>> Cc: Radim Krčmář <rkrc...@redhat.com>
>>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
>>> ---
>>> 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),
>>>
>>
>> What branch should I test this on top of?
>
> Just use whatever you were using before, and revert commit c9db607
> ("UefiCpuPkg: PiSmmCpuDxeSmm: do not execute RSM from 64-bit mode",
> 2015-10-14) from your OVMF branch.
Right, I planned to do that OVMF-side revert; I just wasn't sure if e.g.
kvm/queue had some prerequisite patches for this.
> This is how I tested it, in fact.
I'll try to report back soon.
Thanks!
Laszlo
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