Hi Stefano, > -----Original Message----- > From: Xen-devel <xen-devel-boun...@lists.xenproject.org> On Behalf Of Wei > Chen > Sent: 2022年3月3日 10:07 > To: Julien Grall <jul...@xen.org>; xen-devel@lists.xenproject.org; Stefano > Stabellini <sstabell...@kernel.org> > Cc: Bertrand Marquis <bertrand.marq...@arm.com>; Penny Zheng > <penny.zh...@arm.com>; Henry Wang <henry.w...@arm.com>; nd <n...@arm.com> > Subject: RE: Proposal for Porting Xen to Armv8-R64 - DraftA > > Hi Julien, > > > -----Original Message----- > > From: Julien Grall <jul...@xen.org> > > Sent: 2022年3月2日 20:00 > > To: Wei Chen <wei.c...@arm.com>; xen-devel@lists.xenproject.org; Stefano > > Stabellini <sstabell...@kernel.org> > > Cc: Bertrand Marquis <bertrand.marq...@arm.com>; Penny Zheng > > <penny.zh...@arm.com>; Henry Wang <henry.w...@arm.com>; nd <n...@arm.com> > > Subject: Re: Proposal for Porting Xen to Armv8-R64 - DraftA > > > > > > > > On 01/03/2022 07:51, Wei Chen wrote: > > > Hi Julien, > > > > Hi Wei, > > > > >> -----Original Message----- > > >> From: Julien Grall <jul...@xen.org> > > >> Sent: 2022年2月26日 4:55 > > >> To: Wei Chen <wei.c...@arm.com>; xen-devel@lists.xenproject.org; > > Stefano > > >> Stabellini <sstabell...@kernel.org> > > >> Cc: Bertrand Marquis <bertrand.marq...@arm.com>; Penny Zheng > > >> <penny.zh...@arm.com>; Henry Wang <henry.w...@arm.com>; nd > <n...@arm.com> > > >> Subject: Re: Proposal for Porting Xen to Armv8-R64 - DraftA > > >>> ### 1.2. Xen Challenges with PMSA Virtualization > > >>> Xen is PMSA unaware Type-1 Hypervisor, it will need modifications to > > run > > >>> with an MPU and host multiple guest OSes. > > >>> > > >>> - No MMU at EL2: > > >>> - No EL2 Stage 1 address translation > > >>> - Xen provides fixed ARM64 virtual memory layout as basis > of > > >> EL2 > > >>> stage 1 address translation, which is not applicable on > > MPU > > >> system, > > >>> where there is no virtual addressing. As a result, any > > >> operation > > >>> involving transition from PA to VA, like ioremap, needs > > >> modification > > >>> on MPU system. > > >>> - Xen's run-time addresses are the same as the link time > > addresses. > > >>> - Enable PIC (position-independent code) on a real-time > > target > > >>> processor probably very rare. > > >> > > >> Aside the assembly boot code and UEFI stub, Xen already runs at the > > same > > >> address as it was linked. > > >> > > > > > > But the difference is that, base on MMU, we can use the same link > > address > > > for all platforms. But on MPU system, we can't do it in the same way. > > > > I agree that we currently use the same link address for all the > > platforms. But this is also a problem when using MMU because EL2 has a > > single TTBR. > > > > At the moment we are switching page-tables with the MMU which is not > > safe. Instead we need to turn out the MMU off, switch page-tables and > > then turn on the MMU. This means we need to have an identity mapping of > > Xen in the page-tables. Assuming Xen is not relocated, the identity > > mapping may clash with Xen (or the rest of the virtual address map). > > > > Is this the same reason we create a dummy reloc section for EFI loader? > > > My initial idea was to enable PIC and update the relocation at boot > > time. But this is a bit cumbersome to do. So now I am looking to have a > > semi-dynamic virtual layout and find some place to relocate part of Xen > > to use for CPU bring-up. > > > > Anyway, my point is we possibly could look at PIC if that could allow > > generic Xen image. > > > > I understand your concern. IMO, PIC is possible to do this, but obviously, > it's not a small amount of work. And I want to hear some suggestions from > Stefano, because he also has some solutions in previous thread. >
Can you have a look at the PIC discussion between Julien and me? I think we may need some inputs from your view. Thanks, Wei Chen [...]
