From: Sean Christopherson <seanjc@google.com>
To: David Hildenbrand <david@redhat.com>
Cc: Emanuele Giuseppe Esposito <eesposit@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Maxim Levitsky <mlevitsk@redhat.com>,
kvm@vger.kernel.org, Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, Like Xu <like.xu.linux@gmail.com>
Subject: Re: [RFC PATCH 0/9] kvm: implement atomic memslot updates
Date: Mon, 26 Sep 2022 21:28:38 +0000 [thread overview]
Message-ID: <YzIZhn47brWBfQah@google.com> (raw)
In-Reply-To: <14d5b8f2-7cb6-ce24-c7a7-32aa9117c953@redhat.com>
On Mon, Sep 26, 2022, David Hildenbrand wrote:
> On 23.09.22 15:38, Emanuele Giuseppe Esposito wrote:
> >
> >
> > Am 23/09/2022 um 15:21 schrieb David Hildenbrand:
> > > On 23.09.22 15:10, Emanuele Giuseppe Esposito wrote:
> > > >
> > > >
> > > > Am 19/09/2022 um 19:30 schrieb David Hildenbrand:
> > > > > On 19.09.22 09:53, David Hildenbrand wrote:
> > > > > > On 18.09.22 18:13, Emanuele Giuseppe Esposito wrote:
> > > > > > >
> > > > > > >
> > > > > > > Am 09/09/2022 um 16:30 schrieb Sean Christopherson:
> > > > > > > > On Fri, Sep 09, 2022, Emanuele Giuseppe Esposito wrote:
> > > > > > > > > KVM is currently capable of receiving a single memslot update
> > > > > > > > > through
> > > > > > > > > the KVM_SET_USER_MEMORY_REGION ioctl.
> > > > > > > > > The problem arises when we want to atomically perform multiple
> > > > > > > > > updates,
> > > > > > > > > so that readers of memslot active list avoid seeing incomplete
> > > > > > > > > states.
> > > > > > > > >
> > > > > > > > > For example, in RHBZ
> > > > > > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1979276
...
> As Sean said "This is an awful lot of a complexity to take on for something
> that appears to be solvable in userspace."
And if the userspace solution is unpalatable for whatever reason, I'd like to
understand exactly what KVM behavior is problematic for userspace. E.g. the
above RHBZ bug should no longer be an issue as the buggy commit has since been
reverted.
If the issue is KVM doing something nonsensical on a code fetch to MMIO, then I'd
much rather fix _that_ bug and improve KVM's user exit ABI to let userspace handle
the race _if_ userspace chooses not to pause vCPUs.
next prev parent reply other threads:[~2022-09-26 21:28 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-09 10:44 [RFC PATCH 0/9] kvm: implement atomic memslot updates Emanuele Giuseppe Esposito
2022-09-09 10:44 ` [RFC PATCH 1/9] kvm_main.c: move slot check in kvm_set_memory_region Emanuele Giuseppe Esposito
2022-09-28 16:41 ` Paolo Bonzini
2022-09-09 10:44 ` [RFC PATCH 2/9] kvm.h: introduce KVM_SET_USER_MEMORY_REGION_LIST ioctl Emanuele Giuseppe Esposito
2022-09-28 16:42 ` Paolo Bonzini
2022-09-09 10:45 ` [RFC PATCH 3/9] kvm_main.c: introduce kvm_internal_memory_region_list Emanuele Giuseppe Esposito
2022-09-28 16:48 ` Paolo Bonzini
2022-09-09 10:45 ` [RFC PATCH 4/9] kvm_main.c: split logic in kvm_set_memslots Emanuele Giuseppe Esposito
2022-09-28 17:04 ` Paolo Bonzini
2022-09-09 10:45 ` [RFC PATCH 5/9] kvm_main.c: split __kvm_set_memory_region logic in kvm_check_mem and kvm_prepare_batch Emanuele Giuseppe Esposito
2022-09-13 2:56 ` Yang, Weijiang
2022-09-18 16:22 ` Emanuele Giuseppe Esposito
2022-09-28 17:11 ` Paolo Bonzini
2022-09-09 10:45 ` [RFC PATCH 6/9] kvm_main.c: simplify change-specific callbacks Emanuele Giuseppe Esposito
2022-09-09 10:45 ` [RFC PATCH 7/9] kvm_main.c: duplicate invalid memslot also in inactive list Emanuele Giuseppe Esposito
2022-09-28 17:18 ` Paolo Bonzini
2022-09-09 10:45 ` [RFC PATCH 8/9] kvm_main.c: find memslots from the inactive memslot list Emanuele Giuseppe Esposito
2022-09-09 10:45 ` [RFC PATCH 9/9] kvm_main.c: handle atomic memslot update Emanuele Giuseppe Esposito
2022-09-13 2:30 ` Yang, Weijiang
2022-09-18 16:18 ` Emanuele Giuseppe Esposito
2022-09-27 7:46 ` David Hildenbrand
2022-09-27 8:35 ` Emanuele Giuseppe Esposito
2022-09-27 9:22 ` David Hildenbrand
2022-09-27 9:32 ` Emanuele Giuseppe Esposito
2022-09-27 14:52 ` David Hildenbrand
2022-09-28 17:29 ` Paolo Bonzini
2022-09-09 14:30 ` [RFC PATCH 0/9] kvm: implement atomic memslot updates Sean Christopherson
2022-09-18 16:13 ` Emanuele Giuseppe Esposito
2022-09-19 7:38 ` Like Xu
2022-09-19 7:53 ` David Hildenbrand
2022-09-19 17:30 ` David Hildenbrand
2022-09-23 13:10 ` Emanuele Giuseppe Esposito
2022-09-23 13:21 ` David Hildenbrand
2022-09-23 13:38 ` Emanuele Giuseppe Esposito
2022-09-26 9:03 ` David Hildenbrand
2022-09-26 21:28 ` Sean Christopherson [this message]
2022-09-27 7:38 ` Emanuele Giuseppe Esposito
2022-09-27 15:58 ` Sean Christopherson
2022-09-28 9:11 ` Emanuele Giuseppe Esposito
2022-09-28 11:14 ` Maxim Levitsky
2022-09-28 12:52 ` David Hildenbrand
2022-09-28 15:07 ` Paolo Bonzini
2022-09-28 15:33 ` David Hildenbrand
2022-09-28 15:58 ` Sean Christopherson
2022-09-28 16:38 ` Paolo Bonzini
2022-09-28 20:41 ` Sean Christopherson
2022-09-29 8:05 ` Emanuele Giuseppe Esposito
2022-09-29 8:24 ` David Hildenbrand
2022-09-29 15:18 ` Sean Christopherson
2022-09-29 15:41 ` Paolo Bonzini
2022-09-29 15:28 ` Paolo Bonzini
2022-09-29 15:40 ` Maxim Levitsky
2022-09-29 16:00 ` David Hildenbrand
2022-09-29 21:39 ` Sean Christopherson
2022-10-13 7:43 ` Emanuele Giuseppe Esposito
2022-10-13 8:44 ` David Hildenbrand
2022-10-13 11:12 ` Emanuele Giuseppe Esposito
2022-10-13 14:45 ` David Hildenbrand
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