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a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1626189642; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=gR5bqz+wSeIF9u3YneTgsLIBC29UB9Z6ixAunk7BI50=; b=SIIH8e84Ci4ZS6no30RYiAWiw94N1TinmPXyEMQ2BvAoSC8gZHoWQDlp5TwU2TKUFCRALC oAs9DM6YSYbUeSJzFJ6cfmMBEaCawPqW/yvzEZ2KVKHqs5sRk+Fb4njRkJKHTqNq77+Syi PD5ZMKNehOuVXcjOaJMn5Bn8XebVN/I= Subject: Re: [PATCH] stubdom: foreignmemory: Fix build after 0dbb4be739c5 To: Julien Grall , Jan Beulich Cc: Julien Grall , Ian Jackson , Wei Liu , xen-devel@lists.xenproject.org, Andrew Cooper , Costin Lupu References: <20210713092019.7379-1-julien@xen.org> <0698e4b1-8fb9-919e-e9a2-1b135a808e3e@suse.com> <756ba923-17a6-0889-cc7e-bcd43a5eb258@citrix.com> <3505f2da-4c41-f5ca-d775-814d038d5bad@xen.org> <3c819563-b354-5527-050d-f698324d6021@xen.org> <65d35862-304c-7fe3-82de-3ff62f06529a@suse.com> <40c00267-60d2-c0fc-cde4-8ac4ce936f87@suse.com> <69c62b4c-b46f-9eab-8dfd-742c07423424@suse.com> From: Juergen Gross Message-ID: <7fab704a-6b59-1e9b-663e-a3afdfcc319f@suse.com> Date: Tue, 13 Jul 2021 17:20:41 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="b29Uzl3jyIdMKcrPV5SdZCKA5DN1UHEFi" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --b29Uzl3jyIdMKcrPV5SdZCKA5DN1UHEFi Content-Type: multipart/mixed; boundary="n2TvMf4ohvVdaE1a6L8RtH65yvicFtrmR"; protected-headers="v1" From: Juergen Gross To: Julien Grall , Jan Beulich Cc: Julien Grall , Ian Jackson , Wei Liu , xen-devel@lists.xenproject.org, Andrew Cooper , Costin Lupu Message-ID: <7fab704a-6b59-1e9b-663e-a3afdfcc319f@suse.com> Subject: Re: [PATCH] stubdom: foreignmemory: Fix build after 0dbb4be739c5 References: <20210713092019.7379-1-julien@xen.org> <0698e4b1-8fb9-919e-e9a2-1b135a808e3e@suse.com> <756ba923-17a6-0889-cc7e-bcd43a5eb258@citrix.com> <3505f2da-4c41-f5ca-d775-814d038d5bad@xen.org> <3c819563-b354-5527-050d-f698324d6021@xen.org> <65d35862-304c-7fe3-82de-3ff62f06529a@suse.com> <40c00267-60d2-c0fc-cde4-8ac4ce936f87@suse.com> <69c62b4c-b46f-9eab-8dfd-742c07423424@suse.com> In-Reply-To: --n2TvMf4ohvVdaE1a6L8RtH65yvicFtrmR Content-Type: multipart/mixed; boundary="------------E95AD78BA905F755E19F940D" Content-Language: en-US This is a multi-part message in MIME format. --------------E95AD78BA905F755E19F940D Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 13.07.21 17:15, Julien Grall wrote: > Hi Juergen, >=20 > On 13/07/2021 16:09, Juergen Gross wrote: >> On 13.07.21 16:38, Julien Grall wrote: >>> Hi Juergen, >>> >>> On 13/07/2021 15:23, Juergen Gross wrote: >>>> On 13.07.21 16:19, Julien Grall wrote: >>>>> Hi Jan, >>>>> >>>>> On 13/07/2021 15:14, Jan Beulich wrote: >>>>>>> And I don't think it should be named XC_PAGE_*, but rather=20 >>>>>>> XEN_PAGE_*. >>>>>> >>>>>> Even that doesn't seem right to me, at least in principle. There=20 >>>>>> shouldn't >>>>>> be a build time setting when it may vary at runtime. IOW on Arm I = >>>>>> think a >>>>>> runtime query to the hypervisor would be needed instead. >>>>> >>>>> Yes, we want to be able to use the same userspace/OS without=20 >>>>> rebuilding to a specific hypervisor page size. >>>> >>>> This define is used for accessing data of other domains. See the def= ine >>>> for XEN_PAGE_SIZE in xen/include/public/io/ring.h >>>> >>>> So it should be a constant (minimal) page size for all hypervisors a= nd >>>> guests of an architecture. >>> >>> Do you mean the maximum rather than minimal? If you use the minimal=20 >>> (4KB), then you would not be able to map the page in the stage-2 if=20 >>> the hypervisor is using 64KB. >> >> But this would mean that the current solution to use XC_PAGE_SIZE is >> wrong, as this is 4k. >=20 > The existing ABI is implicitely based on using the hypervisor page=20 > granularity (currently 4KB). >=20 > There is really no way we can support existing guest on 64KB hypervisor= =2E=20 > But if we were going to break them, then we should consider to do one o= f=20 > the following option: > =C2=A0=C2=A0 1) use 64KB page granularity for ABI > =C2=A0=C2=A0 2) query the hypervisor page granularity at runtime >=20 > The ideal is 2) because it is more scalable for the future. We also nee= d=20 > to consider to extend the PV protocol so the backend and frontend can=20 > agree on the page size. I absolutely agree, but my suggestion was to help finding a proper way to cleanup the current interface mess. And this should be done the way I suggested IMO. A later interface extension for future guests can still be done on top of that. 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