From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
David Hildenbrand <david@redhat.com>
Cc: 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: Tue, 27 Sep 2022 09:38:46 +0200 [thread overview]
Message-ID: <3b04db9d-0177-7e6e-a54c-a28ada8b1d36@redhat.com> (raw)
In-Reply-To: <YzIZhn47brWBfQah@google.com>
Am 26/09/2022 um 23:28 schrieb Sean Christopherson:
> 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.
It still is because I can reproduce the bug, as also pointed out in
multiple comments below.
>
> 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.
>
Also on the BZ they all seem (Paolo included) to agree that the issue is
non-atomic memslots update.
To be more precise, what I did mostly follows what Peter explained in
comment 19 : https://bugzilla.redhat.com/show_bug.cgi?id=1979276#c19
next prev parent reply other threads:[~2022-09-27 7:39 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-09 10:44 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
2022-09-27 7:38 ` Emanuele Giuseppe Esposito [this message]
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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