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From: Marc Zyngier <maz@kernel.org>
To: Anastassios Nanos <ananos@nubificus.co.uk>
Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
	linux-kernel@vger.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>,
	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>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 0/2] Expose KVM API to Linux Kernel
Date: Mon, 18 May 2020 08:50:42 +0100	[thread overview]
Message-ID: <c1124c27293769f8e4836fb8fdbd5adf@kernel.org> (raw)
In-Reply-To: <cover.1589784221.git.ananos@nubificus.co.uk>

On 2020-05-18 07:58, Anastassios Nanos wrote:
> To spawn KVM-enabled Virtual Machines on Linux systems, one has to use
> QEMU, or some other kind of VM monitor in user-space to host the vCPU
> threads, I/O threads and various other book-keeping/management 
> mechanisms.
> This is perfectly fine for a large number of reasons and use cases: for
> instance, running generic VMs, running general purpose Operating 
> systems
> that need some kind of emulation for legacy boot/hardware etc.
> What if we wanted to execute a small piece of code as a guest instance,
> without the involvement of user-space? The KVM functions are already 
> doing
> what they should: VM and vCPU setup is already part of the kernel, the 
> only
> missing piece is memory handling.
> With these series, (a) we expose to the Linux Kernel the bare minimum 
> API functions in order to spawn a guest instance without the 
> intervention
> of user-space; and (b) we tweak the memory handling code of KVM-related
> functions to account for another kind of guest, spawned in 
> kernel-space.
> PATCH #1 exposes the needed stub functions, whereas PATCH #2 introduces 
> the
> changes in the KVM memory handling code for x86_64 and aarch64.
> An example of use is provided based on kvmtest.c
> [https://lwn.net/Articles/658512/] at
> https://github.com/cloudkernels/kvmmtest

You don't explain *why* we would want this. What is the overhead of 
a userspace if your guest doesn't need any userspace handling? The 
example indeed shows that the KVM userspace API is usable  without any 
of emulation, hence has almost no cost.

Without a clear description of the advantages of your solution, as well
as a full featured in-tree use case, I find it pretty hard to support 


Jazz is not dead. It just smells funny...

  parent reply	other threads:[~2020-05-18  7:50 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 ` Marc Zyngier [this message]
     [not found]   ` <CALRTab90UyMq2hMxCdCmC3GwPWFn2tK_uKMYQP2YBRcHwzkEUQ@mail.gmail.com>
2020-05-18 11:18     ` [PATCH 0/2] Expose KVM API to Linux Kernel 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
2020-05-18  9:38     ` Thomas Gleixner

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