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From: Jarkko Sakkinen <jarkko@kernel.org>
To: Sean Christopherson <seanjc@google.com>
Cc: Kai Huang <kai.huang@intel.com>,
	linux-sgx@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org,
	luto@kernel.org, dave.hansen@intel.com, haitao.huang@intel.com,
	pbonzini@redhat.com, bp@alien8.de, tglx@linutronix.de,
	mingo@redhat.com, hpa@zytor.com, jmattson@google.com,
	joro@8bytes.org, vkuznets@redhat.com, wanpengli@tencent.com
Subject: Re: [RFC PATCH v2 15/26] KVM: VMX: Convert vcpu_vmx.exit_reason to a union
Date: Thu, 21 Jan 2021 02:47:07 +0200	[thread overview]
Message-ID: <YAjPC5VTiyO3XFsJ@kernel.org> (raw)
In-Reply-To: <YAhcvqXNxq0ALCyO@google.com>

On Wed, Jan 20, 2021 at 08:39:26AM -0800, Sean Christopherson wrote:
> On Wed, Jan 20, 2021, Jarkko Sakkinen wrote:
> > On Mon, Jan 18, 2021 at 04:28:26PM +1300, Kai Huang wrote:
> > > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > > 
> > > Convert vcpu_vmx.exit_reason from a u32 to a union (of size u32).  The
> > > full VM_EXIT_REASON field is comprised of a 16-bit basic exit reason in
> > > bits 15:0, and single-bit modifiers in bits 31:16.
> > > 
> > > Historically, KVM has only had to worry about handling the "failed
> > > VM-Entry" modifier, which could only be set in very specific flows and
> > > required dedicated handling.  I.e. manually stripping the FAILED_VMENTRY
> > > bit was a somewhat viable approach.  But even with only a single bit to
> > > worry about, KVM has had several bugs related to comparing a basic exit
> > > reason against the full exit reason store in vcpu_vmx.
> > > 
> > > Upcoming Intel features, e.g. SGX, will add new modifier bits that can
> > > be set on more or less any VM-Exit, as opposed to the significantly more
> > > restricted FAILED_VMENTRY, i.e. correctly handling everything in one-off
> > > flows isn't scalable.  Tracking exit reason in a union forces code to
> > > explicitly choose between consuming the full exit reason and the basic
> > > exit, and is a convenient way to document and access the modifiers.
> > > 
> > > No functional change intended.
> > > 
> > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > > Signed-off-by: Kai Huang <kai.huang@intel.com>
> > > ---
> > >  arch/x86/kvm/vmx/nested.c | 42 +++++++++++++++---------
> > >  arch/x86/kvm/vmx/vmx.c    | 68 ++++++++++++++++++++-------------------
> > >  arch/x86/kvm/vmx/vmx.h    | 25 +++++++++++++-
> > >  3 files changed, 86 insertions(+), 49 deletions(-)
> > > 
> > > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > > index 0fbb46990dfc..f112c2482887 100644
> > > --- a/arch/x86/kvm/vmx/nested.c
> > > +++ b/arch/x86/kvm/vmx/nested.c
> > > @@ -3311,7 +3311,11 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
> > >  	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> > >  	enum vm_entry_failure_code entry_failure_code;
> > >  	bool evaluate_pending_interrupts;
> > > -	u32 exit_reason, failed_index;
> > > +	u32 failed_index;
> > > +	union vmx_exit_reason exit_reason = {
> > > +		.basic = -1,
> > > +		.failed_vmentry = 1,
> > > +	};
> > 
> > Instead, put this declaration to the correct place, following the
> > reverse christmas tree ordering:
> > 
> >         union vmx_exit_reason exit_reason = {};
> > 
> > And after declarations:
> > 
> >         exit_reason.basic = -1;
> >         exit_reason.failed_vmentry = 1;
> > 
> > More pleasing for the eye.
> 
> I disagree (obviously, since I wrote the patch).  Initializing the fields to
> their respective values is a critical, but subtle, aspect of this code.  Making
> the code stand out via explicit initialization is a good thing, and we really
> don't want any possibility of code touching exit_reason before it is initialized.

The struct does get initialized to zero, and fields get initialized
to their respective values. What is the critical aspect that is gone?
I'm not following.

/Jarkko

  reply	other threads:[~2021-01-21  0:52 UTC|newest]

Thread overview: 91+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-18  3:26 [RFC PATCH v2 00/26] KVM SGX virtualization support Kai Huang
2021-01-18  3:26 ` [RFC PATCH v2 01/26] x86/cpufeatures: Add SGX1 and SGX2 sub-features Kai Huang
2021-01-19 16:19   ` Borislav Petkov
2021-01-19 18:03     ` Sean Christopherson
2021-01-19 22:54       ` Kai Huang
2021-01-20 10:28       ` Borislav Petkov
2021-01-20 11:50   ` Jarkko Sakkinen
2021-01-20 23:23     ` Kai Huang
2021-01-21  1:01       ` Jarkko Sakkinen
2021-01-18  3:26 ` [RFC PATCH v2 02/26] x86/sgx: Remove a warn from sgx_free_epc_page() Kai Huang
2021-01-19  8:32   ` Jarkko Sakkinen
2021-01-20  0:42     ` Kai Huang
2021-01-18  3:26 ` [RFC PATCH v2 03/26] x86/sgx: Wipe out EREMOVE " Kai Huang
2021-01-18  3:26 ` [RFC PATCH v2 04/26] x86/sgx: Add SGX_CHILD_PRESENT hardware error code Kai Huang
2021-01-20 11:51   ` Jarkko Sakkinen
2021-01-18  3:26 ` [RFC PATCH v2 05/26] x86/sgx: Introduce virtual EPC for use by KVM guests Kai Huang
2021-01-20 11:54   ` Jarkko Sakkinen
2021-01-20 17:40     ` Sean Christopherson
2021-01-21  0:54       ` Jarkko Sakkinen
2021-01-21  0:55         ` Jarkko Sakkinen
2021-01-18  3:27 ` [RFC PATCH v2 06/26] x86/cpu/intel: Allow SGX virtualization without Launch Control support Kai Huang
2021-01-20 21:02   ` Dave Hansen
2021-01-20 22:36     ` Sean Christopherson
2021-01-20 23:27       ` Dave Hansen
2021-01-20 23:48         ` Kai Huang
2021-01-20 23:51           ` Dave Hansen
2021-01-21  1:53             ` Kai Huang
2021-01-21 14:35               ` Jarkko Sakkinen
2021-01-21  1:12         ` Jarkko Sakkinen
2021-01-20 23:50     ` Kai Huang
2021-01-21  1:11     ` Jarkko Sakkinen
2021-01-18  3:27 ` [RFC PATCH v2 07/26] x86/sgx: Initialize virtual EPC driver even when SGX driver is disabled Kai Huang
2021-01-18  3:27 ` [RFC PATCH v2 08/26] x86/sgx: Expose SGX architectural definitions to the kernel Kai Huang
2021-01-20 11:58   ` Jarkko Sakkinen
2021-01-20 23:53     ` Kai Huang
2021-01-18  3:27 ` [RFC PATCH v2 09/26] x86/sgx: Move ENCLS leaf definitions to sgx_arch.h Kai Huang
2021-01-20 11:59   ` Jarkko Sakkinen
2021-01-18  3:28 ` [RFC PATCH v2 10/26] x86/sgx: Add SGX2 ENCLS leaf definitions (EAUG, EMODPR and EMODT) Kai Huang
2021-01-20 11:59   ` Jarkko Sakkinen
2021-01-18  3:28 ` [RFC PATCH v2 11/26] x86/sgx: Add encls_faulted() helper Kai Huang
2021-01-20 12:03   ` Jarkko Sakkinen
2021-01-20 23:43     ` Kai Huang
2021-01-21  1:08       ` Jarkko Sakkinen
2021-01-21  1:12         ` Kai Huang
2021-01-21 14:38           ` Jarkko Sakkinen
2021-01-18  3:28 ` [RFC PATCH v2 12/26] x86/sgx: Add helper to update SGX_LEPUBKEYHASHn MSRs Kai Huang
2021-01-20 12:03   ` Jarkko Sakkinen
2021-01-20 18:36     ` Dave Hansen
2021-01-20 23:36       ` Kai Huang
2021-01-20 23:50         ` Dave Hansen
2021-01-21  1:06           ` Kai Huang
2021-01-21  1:15             ` Dave Hansen
2021-01-21  1:44               ` Kai Huang
2021-01-21 14:36                 ` Jarkko Sakkinen
2021-01-21  1:18             ` Kai Huang
2021-01-21  1:09         ` Jarkko Sakkinen
2021-01-21  1:08       ` Jarkko Sakkinen
2021-01-18  3:28 ` [RFC PATCH v2 13/26] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM Kai Huang
2021-01-20 12:04   ` Jarkko Sakkinen
2021-01-20 23:29     ` Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 14/26] x86/sgx: Move provisioning device creation out of SGX driver Kai Huang
2021-01-20 14:09   ` Jarkko Sakkinen
2021-01-20 23:24     ` Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 15/26] KVM: VMX: Convert vcpu_vmx.exit_reason to a union Kai Huang
2021-01-20 14:18   ` Jarkko Sakkinen
2021-01-20 16:39     ` Sean Christopherson
2021-01-21  0:47       ` Jarkko Sakkinen [this message]
2021-01-21 16:33         ` Sean Christopherson
2021-01-22 17:29           ` Jarkko Sakkinen
2021-01-18  3:28 ` [RFC PATCH v2 16/26] KVM: x86: Export kvm_mmu_gva_to_gpa_{read,write}() for SGX (VMX) Kai Huang
2021-01-20 14:19   ` Jarkko Sakkinen
2021-01-18  3:28 ` [RFC PATCH v2 17/26] KVM: x86: Define new #PF SGX error code bit Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 18/26] KVM: x86: Add support for reverse CPUID lookup of scattered features Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 19/26] KVM: x86: Add reverse-CPUID lookup support for scattered SGX features Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 20/26] KVM: VMX: Add basic handling of VM-Exit from SGX enclave Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 21/26] KVM: VMX: Frame in ENCLS handler for SGX virtualization Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 22/26] KVM: VMX: Add SGX ENCLS[ECREATE] handler to enforce CPUID restrictions Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 23/26] KVM: VMX: Add emulation of SGX Launch Control LE hash MSRs Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 24/26] KVM: VMX: Add ENCLS[EINIT] handler to support SGX Launch Control (LC) Kai Huang
2021-01-18  3:28 ` [RFC PATCH v2 25/26] KVM: VMX: Enable SGX virtualization for SGX1, SGX2 and LC Kai Huang
2021-01-18  3:29 ` [RFC PATCH v2 26/26] KVM: x86: Add capability to grant VM access to privileged SGX attribute Kai Huang
2021-01-19  8:23 ` [RFC PATCH v2 00/26] KVM SGX virtualization support Jarkko Sakkinen
2021-01-20  0:52   ` Kai Huang
2021-01-20 16:35     ` Sean Christopherson
2021-01-20 16:39       ` Paolo Bonzini
2021-01-21  1:28         ` Kai Huang
2021-01-20 23:43     ` Jarkko Sakkinen
2021-01-20 23:52       ` Kai Huang
2021-01-21  1:16         ` Jarkko Sakkinen
2021-01-21  1:27           ` Kai Huang
2021-01-21 14:34             ` Jarkko Sakkinen

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