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From: Sean Christopherson <seanjc@google.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
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: Wed, 20 Jan 2021 08:39:26 -0800	[thread overview]
Message-ID: <YAhcvqXNxq0ALCyO@google.com> (raw)
In-Reply-To: <YAg7vzevfw5iL9kN@kernel.org>

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.

  reply	other threads:[~2021-01-20 16:45 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 [this message]
2021-01-21  0:47       ` Jarkko Sakkinen
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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