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Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux

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On Mon, 2015-09-14 at 17:23 +0200, Roger Pau Monné wrote:
> I'm not saying that we shouldn't take those patches, I'm just saying
> that IMHO this is a workaround, and I would like to see a plan and
> somebody committed to have it fixed in a proper way, by introducing a
> 64KB PV block protocol.

In my view the basic unit of operation for all Xen interfaces (on x86 and
arm at least[0]) is 4K. The peer at either end of a PV protocol should
therefore be entitled to assume that at a minimum the other end supports
operation in 4K mode (i.e. 4K is the baseline).

Operations in larger sizes (which would necessarily be multiples of 4K) are
then an extension which is subject to a negotiation between the two ends,
it doesn't really matter if those larger sizes arise because of the use of
superpages or because the guest is internally using some larger basic page
size (which ARM calls a "granule", and where 64K comes from here).

I think this line of reasoning applies just as strongly to the hypercall
ABI as well BTW, they all use 4K as their basic unit, but might support
extensions to operation on multiples of that (negotiated either via a
specific error return and fallback or via the use of XENFEAT).

Ian.

[0] It's not implausible that some other architecture may exsit which
doesn't use 4K as the basic page szie)
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[PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:40 +0200
  [PATCH v4 12/20] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:40 +0200
    Re: [PATCH v4 12/20] xen/balloon: Don't rely on the page granularity  is the same for Xen and Linux Stefano Stabellini <stefano.stabellini@eu.citrix.com> - 2015-09-07 18:50 +0200
  [PATCH v4 15/20] block/xen-blkfront: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:50 +0200
  [PATCH v4 20/20] arm/xen: Add support for 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:50 +0200
  [PATCH v4 17/20] net/xen-netfront: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:50 +0200
  [PATCH v4 10/20] xen/xenbus: Use Xen page definition Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:50 +0200
  [PATCH v4 16/20] block/xen-blkback: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:50 +0200
  [PATCH v4 18/20] net/xen-netback: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-07 17:50 +0200
    Re: [PATCH v4 18/20] net/xen-netback: Make it running on 64KB page  granularity Wei Liu <wei.liu2@citrix.com> - 2015-09-07 19:00 +0200
      Re: [Xen-devel] [PATCH v4 18/20] net/xen-netback: Make it running on  64KB page granularity Wei Liu <wei.liu2@citrix.com> - 2015-09-08 13:10 +0200
      Re: [Xen-devel] [PATCH v4 18/20] net/xen-netback: Make it running  on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-08 13:10 +0200
  Re: [Xen-devel] [PATCH v4 00/20] xen/arm64: Add support for 64KB  page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-11 21:50 +0200
  Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Roger Pau Monné <roger.pau@citrix.com> - 2015-09-14 11:00 +0200
    Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-14 12:50 +0200
      Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Roger Pau Monné <roger.pau@citrix.com> - 2015-09-14 13:10 +0200
        Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-14 13:30 +0200
          Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Roger Pau Monné <roger.pau@citrix.com> - 2015-09-14 14:10 +0200
            Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-14 14:50 +0200
              Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Roger Pau Monné <roger.pau@citrix.com> - 2015-09-14 16:40 +0200
                Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-14 16:50 +0200
                Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Stefano Stabellini <stefano.stabellini@eu.citrix.com> - 2015-09-14 17:00 +0200
                Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Roger Pau Monné <roger.pau@citrix.com> - 2015-09-14 17:30 +0200
                Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Ian Campbell <ian.campbell@citrix.com> - 2015-09-22 13:20 +0200
            Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-18 16:20 +0200
        Re: [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Arnd Bergmann <arnd@arndb.de> - 2015-09-14 13:40 +0200
          Re: [Xen-devel] [PATCH v4 00/20] xen/arm64: Add support for 64KB  page in Linux David Vrabel <david.vrabel@citrix.com> - 2015-09-15 15:20 +0200
            Re: [Xen-devel] [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux Arnd Bergmann <arnd@arndb.de> - 2015-09-15 15:30 +0200
  Re: [Xen-devel] [PATCH v4 00/20] xen/arm64: Add support for 64KB  page in Linux David Vrabel <david.vrabel@citrix.com> - 2015-09-29 18:30 +0200
    Re: [Xen-devel] [PATCH v4 00/20] xen/arm64: Add support for 64KB  page in Linux David Vrabel <david.vrabel@citrix.com> - 2015-09-29 18:40 +0200
    Re: [Xen-devel] [PATCH v4 00/20] xen/arm64: Add support for 64KB  page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-29 18:40 +0200

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