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Date: Tue, 26 Mar 2019 15:11:56 +0200
From: Liran Alon <liran.alon@...cle.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Jon Doron <arilou@...il.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: nVMX: allow RSM to restore VMXE CR4 flag
> On 26 Mar 2019, at 15:07, Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> Commit 5bea5123cbf0 ("KVM: VMX: check nested state and CR4.VMXE against
> SMM") introduced a check to vmx_set_cr4() forbidding to set VMXE from SMM.
> The check is correct, however, there is a special case when RSM is called
> to leave SMM: rsm_enter_protected_mode() is called with HF_SMM_MASK still
> set and in case VMXE was set before entering SMM we're failing to return.
>
> Resolve the issue by temporary dropping HF_SMM_MASK around set_cr4() calls
> when ops->set_cr() is called from RSM.
>
> Reported-by: Jon Doron <arilou@...il.com>
> Suggested-by: Liran Alon <liran.alon@...cle.com>
> Fixes: 5bea5123cbf0 ("KVM: VMX: check nested state and CR4.VMXE against SMM")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Patch looks good to me.
Reviewed-by: Liran Alon <liran.alon@...cle.com>
> ---
> - Instread of putting the temporary HF_SMM_MASK drop to
> rsm_enter_protected_mode() (as was suggested by Liran), move it to
> emulator_set_cr() modifying its interface. emulate.c seems to be
> vcpu-specifics-free at this moment, we may want to keep it this way.
> - It seems that Hyper-V+UEFI on KVM is still broken, I'm observing sporadic
> hangs even with this patch. These hangs, however, seem to be unrelated to
> rsm.
Feel free to share details on these hangs ;)
Great work,
-Liran
> ---
> arch/x86/include/asm/kvm_emulate.h | 3 ++-
> arch/x86/kvm/emulate.c | 27 ++++++++++++++-------------
> arch/x86/kvm/x86.c | 12 +++++++++++-
> 3 files changed, 27 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> index 93c4bf598fb0..6c33caa82fa5 100644
> --- a/arch/x86/include/asm/kvm_emulate.h
> +++ b/arch/x86/include/asm/kvm_emulate.h
> @@ -203,7 +203,8 @@ struct x86_emulate_ops {
> void (*set_gdt)(struct x86_emulate_ctxt *ctxt, struct desc_ptr *dt);
> void (*set_idt)(struct x86_emulate_ctxt *ctxt, struct desc_ptr *dt);
> ulong (*get_cr)(struct x86_emulate_ctxt *ctxt, int cr);
> - int (*set_cr)(struct x86_emulate_ctxt *ctxt, int cr, ulong val);
> + int (*set_cr)(struct x86_emulate_ctxt *ctxt, int cr, ulong val,
> + bool from_rsm);
> int (*cpl)(struct x86_emulate_ctxt *ctxt);
> int (*get_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong *dest);
> int (*set_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong value);
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index c338984c850d..a6204105d4d7 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2413,7 +2413,7 @@ static int rsm_enter_protected_mode(struct x86_emulate_ctxt *ctxt,
> cr3 &= ~0xfff;
> }
>
> - bad = ctxt->ops->set_cr(ctxt, 3, cr3);
> + bad = ctxt->ops->set_cr(ctxt, 3, cr3, true);
> if (bad)
> return X86EMUL_UNHANDLEABLE;
>
> @@ -2422,20 +2422,20 @@ static int rsm_enter_protected_mode(struct x86_emulate_ctxt *ctxt,
> * Then enable protected mode. However, PCID cannot be enabled
> * if EFER.LMA=0, so set it separately.
> */
> - bad = ctxt->ops->set_cr(ctxt, 4, cr4 & ~X86_CR4_PCIDE);
> + bad = ctxt->ops->set_cr(ctxt, 4, cr4 & ~X86_CR4_PCIDE, true);
> if (bad)
> return X86EMUL_UNHANDLEABLE;
>
> - bad = ctxt->ops->set_cr(ctxt, 0, cr0);
> + bad = ctxt->ops->set_cr(ctxt, 0, cr0, true);
> if (bad)
> return X86EMUL_UNHANDLEABLE;
>
> if (cr4 & X86_CR4_PCIDE) {
> - bad = ctxt->ops->set_cr(ctxt, 4, cr4);
> + bad = ctxt->ops->set_cr(ctxt, 4, cr4, true);
> if (bad)
> return X86EMUL_UNHANDLEABLE;
> if (pcid) {
> - bad = ctxt->ops->set_cr(ctxt, 3, cr3 | pcid);
> + bad = ctxt->ops->set_cr(ctxt, 3, cr3 | pcid, true);
> if (bad)
> return X86EMUL_UNHANDLEABLE;
> }
> @@ -2581,7 +2581,7 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt)
>
> /* Zero CR4.PCIDE before CR0.PG. */
> if (cr4 & X86_CR4_PCIDE) {
> - ctxt->ops->set_cr(ctxt, 4, cr4 & ~X86_CR4_PCIDE);
> + ctxt->ops->set_cr(ctxt, 4, cr4 & ~X86_CR4_PCIDE, true);
> cr4 &= ~X86_CR4_PCIDE;
> }
>
> @@ -2595,11 +2595,12 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt)
> /* 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));
> + ctxt->ops->set_cr(ctxt, 0, cr0 & ~(X86_CR0_PG | X86_CR0_PE),
> + true);
>
> /* 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);
> + ctxt->ops->set_cr(ctxt, 4, cr4 & ~X86_CR4_PAE, true);
>
> /* And finally go back to 32-bit mode. */
> efer = 0;
> @@ -3131,7 +3132,7 @@ static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt,
> int ret;
> u8 cpl;
>
> - if (ctxt->ops->set_cr(ctxt, 3, tss->cr3))
> + if (ctxt->ops->set_cr(ctxt, 3, tss->cr3, false))
> return emulate_gp(ctxt, 0);
> ctxt->_eip = tss->eip;
> ctxt->eflags = tss->eflags | 2;
> @@ -3331,7 +3332,7 @@ static int emulator_do_task_switch(struct x86_emulate_ctxt *ctxt,
> write_segment_descriptor(ctxt, tss_selector, &next_tss_desc);
> }
>
> - ops->set_cr(ctxt, 0, ops->get_cr(ctxt, 0) | X86_CR0_TS);
> + ops->set_cr(ctxt, 0, ops->get_cr(ctxt, 0) | X86_CR0_TS, false);
> ops->set_segment(ctxt, tss_selector, &next_tss_desc, 0, VCPU_SREG_TR);
>
> if (has_error_code) {
> @@ -3633,7 +3634,7 @@ static int em_movbe(struct x86_emulate_ctxt *ctxt)
>
> static int em_cr_write(struct x86_emulate_ctxt *ctxt)
> {
> - if (ctxt->ops->set_cr(ctxt, ctxt->modrm_reg, ctxt->src.val))
> + if (ctxt->ops->set_cr(ctxt, ctxt->modrm_reg, ctxt->src.val, false))
> return emulate_gp(ctxt, 0);
>
> /* Disable writeback. */
> @@ -3766,7 +3767,7 @@ static int em_clts(struct x86_emulate_ctxt *ctxt)
>
> cr0 = ctxt->ops->get_cr(ctxt, 0);
> cr0 &= ~X86_CR0_TS;
> - ctxt->ops->set_cr(ctxt, 0, cr0);
> + ctxt->ops->set_cr(ctxt, 0, cr0, false);
> return X86EMUL_CONTINUE;
> }
>
> @@ -3866,7 +3867,7 @@ static int em_smsw(struct x86_emulate_ctxt *ctxt)
> static int em_lmsw(struct x86_emulate_ctxt *ctxt)
> {
> ctxt->ops->set_cr(ctxt, 0, (ctxt->ops->get_cr(ctxt, 0) & ~0x0eul)
> - | (ctxt->src.val & 0x0f));
> + | (ctxt->src.val & 0x0f), false);
> ctxt->dst.type = OP_NONE;
> return X86EMUL_CONTINUE;
> }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a419656521b6..f2745e3170b6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5739,7 +5739,8 @@ static unsigned long emulator_get_cr(struct x86_emulate_ctxt *ctxt, int cr)
> return value;
> }
>
> -static int emulator_set_cr(struct x86_emulate_ctxt *ctxt, int cr, ulong val)
> +static int emulator_set_cr(struct x86_emulate_ctxt *ctxt, int cr, ulong val,
> + bool from_rsm)
> {
> struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
> int res = 0;
> @@ -5755,7 +5756,16 @@ static int emulator_set_cr(struct x86_emulate_ctxt *ctxt, int cr, ulong val)
> res = kvm_set_cr3(vcpu, val);
> break;
> case 4:
> + /*
> + * set_cr4() may forbid to set certain flags (e.g. VMXE) from
> + * SMM but we're actually leaving it; temporary drop HF_SMM_MASK
> + * when setting CR4.
> + */
> + if (from_rsm)
> + vcpu->arch.hflags &= ~HF_SMM_MASK;
> res = kvm_set_cr4(vcpu, mk_cr_64(kvm_read_cr4(vcpu), val));
> + if (from_rsm)
> + vcpu->arch.hflags |= HF_SMM_MASK;
> break;
> case 8:
> res = kvm_set_cr8(vcpu, val);
> --
> 2.20.1
>
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