From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laszlo Ersek Subject: Re: [PATCH] KVM: x86: allow RSM from 64-bit mode Date: Tue, 3 Nov 2015 15:02:00 +0100 Message-ID: <5638BE58.6060507@redhat.com> References: <1446557368-9278-1-git-send-email-pbonzini@redhat.com> <5638B94A.2090702@redhat.com> <5638BAC7.2030704@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: stable@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= To: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <5638BAC7.2030704@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 11/03/15 14:46, Paolo Bonzini wrote: >=20 >=20 > 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=3D1, EFER.LMA=3D0). Getting all the way from 64-bit >>> mode to real mode only requires clearing CS.L and CR4.PCIDE. >>> >>> Cc: stable@vger.kernel.org >>> Fixes: 660a5d517aaab9187f93854425c4c63f4a09195c >>> Cc: Laszlo Ersek >>> Cc: Radim Kr=C4=8Dm=C3=A1=C5=99 >>> Signed-off-by: Paolo Bonzini >>> --- >>> 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) >>> =20 >>> /* >>> * Get back to real mode, to prepare a safe state in which to loa= d >>> - * CR0/CR3/CR4/EFER. >>> - * >>> - * CR4.PCIDE must be zero, because it is a 64-bit mode only featu= re. >>> + * CR0/CR3/CR4/EFER. It's all a bit more complicated if the vCPU >>> + * supports long mode. >>> */ >>> + cr4 =3D 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 &=3D ~X86_CR4_PCIDE; >>> + } >>> + >>> + /* A 32-bit code segment is required to clear EFER.LMA. */ >>> + memset(&cs_desc, 0, sizeof(cs_desc)); >>> + cs_desc.type =3D 0xb; >>> + cs_desc.s =3D cs_desc.g =3D cs_desc.p =3D 1; >>> + ctxt->ops->set_segment(ctxt, 0, &cs_desc, 0, VCPU_SREG_CS); >>> + } >>> + >>> + /* For the 64-bit case, this will clear EFER.LMA. */ >>> cr0 =3D 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 =3D 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 =3D 0; >>> ctxt->ops->set_msr(ctxt, MSR_EFER, efer); >>> =20 >>> @@ -4454,7 +4474,7 @@ static const struct opcode twobyte_table[256]= =3D { >>> 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? >=20 > 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= =2E 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