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From: Peter Xu <peterx@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Michael Tsirkin <mst@redhat.com>,
	Julia Suvorova <jsuvorov@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	x86@kernel.org
Subject: Re: [PATCH RFC 0/5] KVM: x86: KVM_MEM_ALLONES memory
Date: Thu, 14 May 2020 18:05:16 -0400	[thread overview]
Message-ID: <20200514220516.GC449815@xz-x1> (raw)
In-Reply-To: <20200514180540.52407-1-vkuznets@redhat.com>

On Thu, May 14, 2020 at 08:05:35PM +0200, Vitaly Kuznetsov wrote:
> The idea of the patchset was suggested by Michael S. Tsirkin.
> 
> PCIe config space can (depending on the configuration) be quite big but
> usually is sparsely populated. Guest may scan it by accessing individual
> device's page which, when device is missing, is supposed to have 'pci
> holes' semantics: reads return '0xff' and writes get discarded. Currently,
> userspace has to allocate real memory for these holes and fill them with
> '0xff'. Moreover, different VMs usually require different memory.
> 
> The idea behind the feature introduced by this patch is: let's have a
> single read-only page filled with '0xff' in KVM and map it to all such
> PCI holes in all VMs. This will free userspace of obligation to allocate
> real memory and also allow us to speed up access to these holes as we
> can aggressively map the whole slot upon first fault.
> 
> RFC. I've only tested the feature with the selftest (PATCH5) on Intel/AMD
> with and wiuthout EPT/NPT. I haven't tested memslot modifications yet.
> 
> Patches are against kvm/next.

Hi, Vitaly,

Could this be done in userspace with existing techniques?

E.g., shm_open() with a handle and fill one 0xff page, then remap it to
anywhere needed in QEMU?

Thanks,

-- 
Peter Xu


  parent reply	other threads:[~2020-05-14 22:05 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-14 18:05 [PATCH RFC 0/5] KVM: x86: KVM_MEM_ALLONES memory Vitaly Kuznetsov
2020-05-14 18:05 ` [PATCH RFC 1/5] KVM: rename labels in kvm_init() Vitaly Kuznetsov
2020-05-14 18:05 ` [PATCH RFC 2/5] KVM: x86: introduce KVM_MEM_ALLONES memory Vitaly Kuznetsov
2020-05-14 19:18   ` Sean Christopherson
2020-05-15  8:24     ` Vitaly Kuznetsov
2020-05-14 18:05 ` [PATCH RFC 3/5] KVM: x86: move kvm_vcpu_gfn_to_memslot() out of try_async_pf() Vitaly Kuznetsov
2020-05-14 18:05 ` [PATCH RFC 4/5] KVM: x86: aggressively map PTEs in KVM_MEM_ALLONES slots Vitaly Kuznetsov
2020-05-14 19:46   ` Sean Christopherson
2020-05-15  8:36     ` Vitaly Kuznetsov
2020-05-15 13:58       ` Sean Christopherson
2020-05-14 18:05 ` [PATCH RFC 5/5] KVM: selftests: add KVM_MEM_ALLONES test Vitaly Kuznetsov
2020-05-14 22:05 ` Peter Xu [this message]
2020-05-14 22:56   ` [PATCH RFC 0/5] KVM: x86: KVM_MEM_ALLONES memory Sean Christopherson
2020-05-14 23:22     ` Peter Xu
2020-05-14 23:32       ` Sean Christopherson
2020-05-15  8:42         ` Vitaly Kuznetsov
2020-05-15  1:03     ` Andy Lutomirski
2020-05-15 11:15       ` Peter Xu

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