From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jim Mattson <jmattson@google.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
kvm list <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Wanpeng Li <wanpengli@tencent.com>, Peter Xu <peterx@redhat.com>,
Julia Suvorova <jsuvorov@redhat.com>,
Andy Lutomirski <luto@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] KVM: x86: introduce KVM_MEM_PCI_HOLE memory
Date: Wed, 5 Aug 2020 20:18:37 -0400 [thread overview]
Message-ID: <20200805201702-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CALMp9eSWsvufDXMuTUR3Fmh91O7tHUaqpDbAoavSMc=prpcDzg@mail.gmail.com>
On Wed, Aug 05, 2020 at 10:05:40AM -0700, Jim Mattson wrote:
> On Tue, Jul 28, 2020 at 7:38 AM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> >
> > 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
> > hole' semantics: reads return '0xff' and writes get discarded. Compared
> > to the already existing KVM_MEM_READONLY, VMM doesn't need to allocate
> > real memory and stuff it with '0xff'.
>
> Note that the bus error semantics described should apply to *any*
> unbacked guest physical addresses, not just addresses in the PCI hole.
> (Typically, this also applies to the standard local APIC page
> (0xfee00xxx) when the local APIC is either disabled or in x2APIC mode,
> which is an area that kvm has had trouble with in the past.)
Well ATM from KVM's POV unbacked -> exit to userspace, right?
Not sure what you are suggesting here ...
--
MST
next prev parent reply other threads:[~2020-08-06 0:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-28 14:37 [PATCH 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory Vitaly Kuznetsov
2020-07-28 14:37 ` [PATCH 1/3] KVM: x86: move kvm_vcpu_gfn_to_memslot() out of try_async_pf() Vitaly Kuznetsov
2020-07-28 14:37 ` [PATCH 2/3] KVM: x86: introduce KVM_MEM_PCI_HOLE memory Vitaly Kuznetsov
2020-08-05 15:18 ` Andrew Jones
2020-08-06 9:08 ` Vitaly Kuznetsov
2020-08-05 17:05 ` Jim Mattson
2020-08-06 0:18 ` Michael S. Tsirkin [this message]
2020-08-06 17:36 ` Jim Mattson
2020-08-06 9:14 ` Vitaly Kuznetsov
2020-07-28 14:37 ` [PATCH 3/3] KVM: selftests: add KVM_MEM_PCI_HOLE test Vitaly Kuznetsov
2020-08-06 0:21 ` [PATCH 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory Michael S. Tsirkin
2020-08-06 9:19 ` Vitaly Kuznetsov
2020-08-06 9:53 ` Michael S. Tsirkin
2020-08-06 11:39 ` Vitaly Kuznetsov
2020-08-06 12:19 ` Michael S. Tsirkin
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