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Sat, 12 Oct 2019 13:09:28 -0400 (EDT) Date: Sat, 12 Oct 2019 19:09:25 +0200 From: Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= To: Andrew Cooper Message-ID: <20191012170925.GC28966@mail-itl> References: <272a9354-bcb4-50a4-a251-6a453221d6e3@citrix.com> <20191012170040.GB28966@mail-itl> MIME-Version: 1.0 In-Reply-To: <20191012170040.GB28966@mail-itl> Subject: Re: [Xen-devel] [PATCH v2 2/2] xen/efi: optionally call SetVirtualAddressMap() X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Konrad Rzeszutek Wilk , George Dunlap , Tim Deegan , Ian Jackson , Julien Grall , Jan Beulich , xen-devel@lists.xenproject.org Content-Type: multipart/mixed; boundary="===============6156308284445187312==" Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" --===============6156308284445187312== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="XWOWbaMNXpFDWE00" Content-Disposition: inline --XWOWbaMNXpFDWE00 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH v2 2/2] xen/efi: optionally call SetVirtualAddressMap() On Sat, Oct 12, 2019 at 07:00:43PM +0200, Marek Marczykowski-G=C3=B3recki w= rote: > On Sat, Oct 12, 2019 at 05:29:34PM +0100, Andrew Cooper wrote: > > On 12/10/2019 15:36, Marek Marczykowski-G=C3=B3recki wrote: > > > SetVirtualAddressMap() can be called only once, > >=20 > > True. > >=20 > > > hence it's incompatible with kexec. > >=20 > > Most certainly not. > >=20 > > Linux unconditionally enters virtual mode, citing a huge slew of EFI > > firmware bugs, and is perfectly capable of kexec-ing on the resulting > > systems. > >=20 > > This is how Xen should behave as well, and I suspect it will have a > > marked improvement on our ability to actually boot on EFI systems. > >=20 > >=20 > > Now - it may be true that Xen is missing some piece of plumbing to allow > > kexec in virtual mode to work, and that is a fine reason to leave a note > > in the text of an EXPERT option noting what what is/isn't expected to > > work (and what may or may not have been tested). > >=20 > > > For this reason, make it an optional feature, depending on > > > !KEXEC. > >=20 > > This presupposes (at Xen's build time) that a kexec'd kernel is going to > > want/need to use runtime services.=C2=A0 I'm not convinced this is > > universally true, >=20 > In fact, as it turned out in the discussion, right now it definitely > can't, as it doesn't get runtime services table (or efi system table or > any other info required for this). So, it looks like it should read "it > might be incompatible with some future Xen implementation of kexec". Specifically, dependency on !KEXEC isn't needed right now. --=20 Best Regards, Marek Marczykowski-G=C3=B3recki Invisible Things Lab A: Because it messes up the order in which people normally read text. 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