kvm.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Anastassios Nanos <ananos@nubificus.co.uk>
Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
	linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 0/2] Expose KVM API to Linux Kernel
Date: Mon, 18 May 2020 11:18:53 +0200	[thread overview]
Message-ID: <87o8qlvbwi.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <CALRTab-mEYtRG4zQbSGoAri+jg8xNL-imODv=MWE330Hkt_t+Q@mail.gmail.com>

Anastassios Nanos <ananos@nubificus.co.uk> writes:

> Moreover, it doesn't involve *any* mode switch at all while printing
> out the result of the  addition of these two registers -- which I
> guess for a simple use-case like this it isn't much.
> But if we were to scale this to a large number of exits (and their
> respective handling in user-space) that would incur significant
> overhead.

Eliminating frequent exits to userspace when the guest is already
running is absolutely fine but eliminating userspace completely, even
for creation of the guest, is something dubious. To create a simple
guest you need just a dozen of IOCTLs, you'll have to find a really,
really good showcase when it makes a difference. 

E.g. I can imagine the following use-case: you need to create a lot of
guests with the same (or almost the same) memory contents and allocating
and populating this memory in userspace takes time. But even in this
use-case, why do you need to terminate your userspace? Or would it be
possible to create guests from a shared memory? (we may not have
copy-on-write capabilities in KVM currently but this doesn't mean they
can't be added).

Alternatively, you may want to mangle vmexit handling somehow and
exiting to userspace seems slow. Fine, let's add eBPF attach points to
KVM and an API to attach eBPF code there.

I'm, however, just guessing. I understand you may not want to reveal
your original idea for some reason but without us understanding what's
really needed I don't see how the change can be reviewed.

-- 
Vitaly


  parent reply	other threads:[~2020-05-18  9:19 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-18  6:58 [PATCH 0/2] Expose KVM API to Linux Kernel Anastassios Nanos
2020-05-18  6:58 ` [PATCH 1/2] KVMM: export needed symbols Anastassios Nanos
2020-05-18  7:41   ` Marc Zyngier
2020-05-18  7:01 ` [PATCH 2/2] KVMM: Memory and interface related changes Anastassios Nanos
2020-05-18  6:59   ` Anastassios Nanos
2020-05-18  9:13   ` kbuild test robot
2020-05-18  9:28   ` kbuild test robot
2020-05-18 10:16   ` kbuild test robot
2020-05-18  7:50 ` [PATCH 0/2] Expose KVM API to Linux Kernel Marc Zyngier
     [not found]   ` <CALRTab90UyMq2hMxCdCmC3GwPWFn2tK_uKMYQP2YBRcHwzkEUQ@mail.gmail.com>
2020-05-18 11:18     ` Paolo Bonzini
2020-05-18 11:34       ` Maxim Levitsky
2020-05-18 11:51         ` Paolo Bonzini
2020-05-18 12:12           ` Maxim Levitsky
2020-05-18 20:45     ` Andy Lutomirski
2020-05-18  8:42 ` Thomas Gleixner
     [not found]   ` <CALRTab-mEYtRG4zQbSGoAri+jg8xNL-imODv=MWE330Hkt_t+Q@mail.gmail.com>
2020-05-18  9:18     ` Vitaly Kuznetsov [this message]
2020-05-18  9:38     ` Thomas Gleixner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87o8qlvbwi.fsf@vitty.brq.redhat.com \
    --to=vkuznets@redhat.com \
    --cc=ananos@nubificus.co.uk \
    --cc=bp@alien8.de \
    --cc=catalin.marinas@arm.com \
    --cc=hpa@zytor.com \
    --cc=james.morse@arm.com \
    --cc=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=julien.thierry.kdev@gmail.com \
    --cc=kvm@vger.kernel.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-kernel@vger.kernel.org \
    --cc=maz@kernel.org \
    --cc=mingo@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=sean.j.christopherson@intel.com \
    --cc=suzuki.poulose@arm.com \
    --cc=tglx@linutronix.de \
    --cc=wanpengli@tencent.com \
    --cc=will@kernel.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).