diff mbox series

[RFC,v6,1/6] KVM: x86: only allow exits disable before vCPUs created

Message ID 20230121020738.2973-2-kechenl@nvidia.com
State New
Headers
Series KVM: x86: add per-vCPU exits disable capability |

Commit Message

Kechen Lu Jan. 21, 2023, 2:07 a.m. UTC 
  From: Sean Christopherson <seanjc@google.com>

Since VMX and SVM both would never update the control bits if exits
are disable after vCPUs are created, only allow setting exits
disable flag before vCPU creation.

Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Kechen Lu <kechenl@nvidia.com>
Cc: stable@vger.kernel.org
---
 Documentation/virt/kvm/api.rst | 1 +
 arch/x86/kvm/x86.c             | 6 ++++++
 2 files changed, 7 insertions(+)

Comments

Greg KH Jan. 21, 2023, 7:28 a.m. UTC | #1 
On Sat, Jan 21, 2023 at 02:07:33AM +0000, Kechen Lu wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> Since VMX and SVM both would never update the control bits if exits
> are disable after vCPUs are created, only allow setting exits
> disable flag before vCPU creation.
> 
> Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Nit, no blank line between fixes and signed-off-by please.

And an RFC on v6?  An RFC usually means "I don't think this is correct
so do not take it".  How can you do that for 6 versions?  And know that
no one will take an RFC series for that reason (or at least I will
not...)

thanks,

greg k-h
Kechen Lu Jan. 22, 2023, 1:48 a.m. UTC | #2 
Hi Greg,

> -----Original Message-----
> From: Greg KH <gregkh@linuxfoundation.org>
> Sent: Friday, January 20, 2023 11:28 PM
> To: Kechen Lu <kechenl@nvidia.com>
> Cc: kvm@vger.kernel.org; seanjc@google.com; pbonzini@redhat.com;
> zhi.wang.linux@gmail.com; chao.gao@intel.com; shaoqin.huang@intel.com;
> vkuznets@redhat.com; linux-kernel@vger.kernel.org;
> stable@vger.kernel.org
> Subject: Re: [RFC PATCH v6 1/6] KVM: x86: only allow exits disable before
> vCPUs created
> 
> External email: Use caution opening links or attachments
> 
> 
> On Sat, Jan 21, 2023 at 02:07:33AM +0000, Kechen Lu wrote:
> > From: Sean Christopherson <seanjc@google.com>
> >
> > Since VMX and SVM both would never update the control bits if exits
> > are disable after vCPUs are created, only allow setting exits disable
> > flag before vCPU creation.
> >
> > Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT
> > intercepts")
> >
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> 
> Nit, no blank line between fixes and signed-off-by please.

Ack.

> 
> And an RFC on v6?  An RFC usually means "I don't think this is correct so do
> not take it".  How can you do that for 6 versions?  And know that no one will
> take an RFC series for that reason (or at least I will
> not...)

Thanks for correcting this, this is my bad. The v2 to v4 revisions, there are big changes 
on the following patches after this prerequisite patch, so I still "RFC" for the design.
But I should drop the "RFC" starting from v5, there are already consensus on the v5 design 
options

Best Regards,
Kechen

> 
> thanks,
> 
> greg k-h
diff mbox series

Patch

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 9807b05a1b57..fb0fcc566d5a 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7087,6 +7087,7 @@  branch to guests' 0x200 interrupt vector.
 :Architectures: x86
 :Parameters: args[0] defines which exits are disabled
 :Returns: 0 on success, -EINVAL when args[0] contains invalid exits
+          or if any vCPU has already been created
 
 Valid bits in args[0] are::
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index da4bbd043a7b..c8ae9c4f9f08 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6227,6 +6227,10 @@  int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)
 			break;
 
+		mutex_lock(&kvm->lock);
+		if (kvm->created_vcpus)
+			goto disable_exits_unlock;
+
 		if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
 			kvm_can_mwait_in_guest())
 			kvm->arch.mwait_in_guest = true;
@@ -6237,6 +6241,8 @@  int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		if (cap->args[0] & KVM_X86_DISABLE_EXITS_CSTATE)
 			kvm->arch.cstate_in_guest = true;
 		r = 0;
+disable_exits_unlock:
+		mutex_unlock(&kvm->lock);
 		break;
 	case KVM_CAP_MSR_PLATFORM_INFO:
 		kvm->arch.guest_can_read_msr_platform_info = cap->args[0];