From: Sean Christopherson <seanjc@google.com>
To: Kai Huang <kai.huang@intel.com>
Cc: Rongqing Li <lirongqing@baidu.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"x86@kernel.org" <x86@kernel.org>, "bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>
Subject: Re: [PATCH] KVM: x86/mmu: Don't create kvm-nx-lpage-re kthread if not itlb_multihit
Date: Thu, 23 Mar 2023 15:40:43 -0700 [thread overview]
Message-ID: <ZBzU6pa7eOgVf0Kf@google.com> (raw)
In-Reply-To: <48616deee4861976f7960f60caf59cbe37a85f1e.camel@intel.com>
On Thu, Mar 23, 2023, Huang, Kai wrote:
> On Thu, 2023-03-23 at 07:20 -0700, Sean Christopherson wrote:
> > On Thu, Mar 23, 2023, lirongqing@baidu.com wrote:
> > > From: Li RongQing <lirongqing@baidu.com>
> > >
> > > if CPU has not X86_BUG_ITLB_MULTIHIT bug, kvm-nx-lpage-re kthread
> > > is not needed to create
> >
> > Unless userspace forces the mitigation to be enabled, which can be done while KVM
> > is running. �
> >
>
> Wondering why does userspace want to force the mitigation to be enabled if CPU
> doesn't have such bug?
It's definitely useful for testing, but the real motivation is so that the
mitgation can be enabled without a kernel reboot (or reloading KVM), i.e. without
having to drain VMs off the host, if it turns out that the host CPU actually is
vulnerable. I.e. to guard against "Nope, not vulnerable! Oh, wait, just kidding!".
next prev parent reply other threads:[~2023-03-23 22:40 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-23 7:18 [PATCH] KVM: x86/mmu: Don't create kvm-nx-lpage-re kthread if not itlb_multihit lirongqing
2023-03-23 14:20 ` Sean Christopherson
2023-03-23 22:32 ` Huang, Kai
2023-03-23 22:40 ` Sean Christopherson [this message]
2023-03-23 23:16 ` Huang, Kai
2023-03-30 8:18 ` Li,Rongqing
2023-03-30 19:19 ` Sean Christopherson
2023-05-02 2:07 ` Robert Hoo
2023-05-05 12:42 ` zhuangel570
2023-05-05 17:44 ` Sean Christopherson
2023-05-06 7:12 ` zhuangel570
2023-05-06 14:59 ` Robert Hoo
2023-05-06 15:30 ` zhuangel570
2023-05-06 14:49 ` Robert Hoo
2023-05-07 1:18 ` Robert Hoo
2023-05-05 17:56 ` Jim Mattson
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