Date: Mon, 26 Aug 2013 13:37:57 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-virtualization@freebsd.org Subject: Re: CFT: nested page table integration with amd64/pmap Message-ID: <kvfemd$9i6$1@ger.gmane.org> In-Reply-To: <5217DAB2.3020204@freebsd.org> References: <CAFgRE9H2n63%2B3GFwWNwE-Zu3gHPBcWhD4g6frB_ksXz=HAXp5w@mail.gmail.com> <kv7dig$id5$1@ger.gmane.org> <5217DAB2.3020204@freebsd.org>
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[-- Attachment #1 --] On 23/08/2013 23:57, Peter Grehan wrote: >> I always wondered about virtualization environments which have pageable >> guest memory - how does the guest kernel handle situations where it >> really needs non-pageable memory? Does is simply "not care" because for >> it the memory access looks just like it isn't paged but is simply very, >> very slow? > > Yes - from the guest's point of view, what it thinks is physical memory > appears wired. > >> What about time-sensitive situations (like the originally >> mentioned PCI-passthrough)? > > PCI passthru is a special case since the h/w requires that the target > of a DMA transfer is present - there is currently no way for the IOMMU > to generate the equivalent of page faults. So, for PCI passthru, all of > guest memory has to be wired host memory. > > For time-sensitive situations, there's not a lot of options other than > forcing guest memory to be wired, since there isn't visibility into the > host without having o/s-specific "tools" that could communicate this > information to the hypervisor. Ok, that is how I understood it also, but I thought that maybe there was some way of telling which guest memory belongs to the kernel and only wire those pages. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlIbPhUACgkQ/QjVBj3/HSzWjwCfcnzArU4Z2B5YSuliqK9/H4Ji GucAoJyfhU5Izyns6FiJDZWuRG66Ki0h =MtW9 -----END PGP SIGNATURE-----
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