Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754221AbbKCOEw (ORCPT ); Tue, 3 Nov 2015 09:04:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35038 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751266AbbKCOEv (ORCPT ); Tue, 3 Nov 2015 09:04:51 -0500 Subject: Re: [PATCH] KVM: x86: allow RSM from 64-bit mode To: Laszlo Ersek , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1446557368-9278-1-git-send-email-pbonzini@redhat.com> <5638B94A.2090702@redhat.com> <5638BAC7.2030704@redhat.com> <5638BE58.6060507@redhat.com> Cc: stable@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= From: Paolo Bonzini Message-ID: <5638BEFA.30907@redhat.com> Date: Tue, 3 Nov 2015 15:04:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <5638BE58.6060507@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3842 Lines: 97 On 03/11/2015 15:02, Laszlo Ersek wrote: > 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: stable@vger.kernel.org >>>> Fixes: 660a5d517aaab9187f93854425c4c63f4a09195c >>>> Cc: Laszlo Ersek >>>> Cc: Radim Krčmář >>>> 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) >>>> >>>> /* >>>> * 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. Indeed, you can use either your "part 2" series or Radim's patches from kvm/queue, it's the same. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/