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.
next prev parent reply other threads:[~2021-01-20 16:43 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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