linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>, Joerg Roedel <joro@8bytes.org>,
	Wanpeng Li <wanpengli@tencent.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH v2 6/6] KVM: nVMX: re-evaluate emulation_required on nested VM exit
Date: Tue, 21 Sep 2021 22:55:26 +0000	[thread overview]
Message-ID: <YUpi3rpTsoQ/dzp6@google.com> (raw)
In-Reply-To: <20210830125539.1768833-7-mlevitsk@redhat.com>

On Mon, Aug 30, 2021, Maxim Levitsky wrote:
> If L1 had invalid state on VM entry (can happen on SMM transactions
> when we enter from real mode, straight to nested guest),
> 
> then after we load 'host' state from VMCS12, the state has to become
> valid again, but since we load the segment registers with
> __vmx_set_segment we weren't always updating emulation_required.

Because I'm an idiot.

> Update emulation_required explicitly at end of load_vmcs12_host_state.

Can you also add

  Reported-by: kernel test robot <oliver.sang@intel.com>

which is how I ended up here, sort of.

Fixes: 816be9e9be8d ("KVM: nVMX: Don't evaluate "emulation required" on nested VM-Exit")

> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---

The below is overkill.  The state after VM-Exit _can't_ be invalid, which was the
whole point of moving to __vmx_set_segment(), I just forgot the minor detail of
clearing emulation_required.  So just:

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index bc6327950657..55ac7211fb37 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4314,6 +4314,12 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
        if (nested_vmx_load_msr(vcpu, vmcs12->vm_exit_msr_load_addr,
                                vmcs12->vm_exit_msr_load_count))
                nested_vmx_abort(vcpu, VMX_ABORT_LOAD_HOST_MSR_FAIL);
+
+       /*
+        * All relevant vmcs12 host state is checked prior to VM-Entry, thus
+        * L1 guest can never be invalid after VM-Exit.
+        */
+       to_vmx(vcpu)->emulation_required = false;
 }
 
 static inline u64 nested_vmx_get_vmcs01_guest_efer(struct vcpu_vmx *vmx)

>  arch/x86/kvm/vmx/nested.c | 2 ++
>  arch/x86/kvm/vmx/vmx.c    | 8 ++++----
>  arch/x86/kvm/vmx/vmx.h    | 1 +
>  3 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 1a05ae83dae5..f915e1ac589c 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4319,6 +4319,8 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
>  	if (nested_vmx_load_msr(vcpu, vmcs12->vm_exit_msr_load_addr,
>  				vmcs12->vm_exit_msr_load_count))
>  		nested_vmx_abort(vcpu, VMX_ABORT_LOAD_HOST_MSR_FAIL);
> +
> +	to_vmx(vcpu)->emulation_required = vmx_emulation_required(vcpu);
>  }
>  
>  static inline u64 nested_vmx_get_vmcs01_guest_efer(struct vcpu_vmx *vmx)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 02d061f5956a..7ff1e1daeb0a 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1323,7 +1323,7 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>  	vmx_prepare_switch_to_host(to_vmx(vcpu));
>  }
>  
> -static bool emulation_required(struct kvm_vcpu *vcpu)
> +bool vmx_emulation_required(struct kvm_vcpu *vcpu)
>  {
>  	return emulate_invalid_guest_state && !vmx_guest_state_valid(vcpu);
>  }
> @@ -1367,7 +1367,7 @@ void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>  	vmcs_writel(GUEST_RFLAGS, rflags);
>  
>  	if ((old_rflags ^ vmx->rflags) & X86_EFLAGS_VM)
> -		vmx->emulation_required = emulation_required(vcpu);
> +		vmx->emulation_required = vmx_emulation_required(vcpu);
>  }
>  
>  u32 vmx_get_interrupt_shadow(struct kvm_vcpu *vcpu)
> @@ -3077,7 +3077,7 @@ void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>  	}
>  
>  	/* depends on vcpu->arch.cr0 to be set to a new value */
> -	vmx->emulation_required = emulation_required(vcpu);
> +	vmx->emulation_required = vmx_emulation_required(vcpu);
>  }
>  
>  static int vmx_get_max_tdp_level(void)
> @@ -3330,7 +3330,7 @@ static void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int
>  {
>  	__vmx_set_segment(vcpu, var, seg);
>  
> -	to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
> +	to_vmx(vcpu)->emulation_required = vmx_emulation_required(vcpu);
>  }
>  
>  static void vmx_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l)
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 4858c5fd95f2..3a587c51a8d1 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -359,6 +359,7 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
>  void vmx_set_host_fs_gs(struct vmcs_host_state *host, u16 fs_sel, u16 gs_sel,
>  			unsigned long fs_base, unsigned long gs_base);
>  int vmx_get_cpl(struct kvm_vcpu *vcpu);
> +bool vmx_emulation_required(struct kvm_vcpu *vcpu);
>  unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu);
>  void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
>  u32 vmx_get_interrupt_shadow(struct kvm_vcpu *vcpu);
> -- 
> 2.26.3
> 

      reply	other threads:[~2021-09-21 22:55 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-30 12:55 [PATCH v2 0/6] KVM: few more SMM fixes Maxim Levitsky
2021-08-30 12:55 ` [PATCH v2 1/6] KVM: SVM: restore the L1 host state prior to resuming nested guest on SMM exit Maxim Levitsky
2021-08-30 12:55 ` [PATCH v2 2/6] KVM: x86: force PDPTR reload " Maxim Levitsky
2021-08-30 12:55 ` [PATCH v2 3/6] KVM: nSVM: call KVM_REQ_GET_NESTED_STATE_PAGES on exit from SMM mode Maxim Levitsky
2021-08-30 12:55 ` [PATCH v2 4/6] KVM: VMX: synthesize invalid VM exit when emulating invalid guest state Maxim Levitsky
2021-08-30 12:55 ` [PATCH v2 5/6] KVM: nVMX: don't fail nested VM entry on invalid guest state if !from_vmentry Maxim Levitsky
2021-10-08 23:37   ` Sean Christopherson
2021-08-30 12:55 ` [PATCH v2 6/6] KVM: nVMX: re-evaluate emulation_required on nested VM exit Maxim Levitsky
2021-09-21 22:55   ` Sean Christopherson [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YUpi3rpTsoQ/dzp6@google.com \
    --to=seanjc@google.com \
    --cc=bp@alien8.de \
    --cc=hpa@zytor.com \
    --cc=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=mlevitsk@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=vkuznets@redhat.com \
    --cc=wanpengli@tencent.com \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).