On Thu, Aug 27, 2015 at 9:29 AM, Jan Beulich <jbeul...@suse.com> wrote:
> >>> On 27.08.15 at 17:10, <daniel.ki...@oracle.com> wrote: > > On Thu, Aug 27, 2015 at 07:12:38AM -0600, Jan Beulich wrote: > >> >>> On 20.07.15 at 16:29, <daniel.ki...@oracle.com> wrote: > >> > /* Copy bootstrap trampoline to low memory, below 1MB. */ > >> > - mov $sym_phys(trampoline_start),%esi > >> > + lea sym_offset(trampoline_start)(%ebp),%esi > >> > mov $trampoline_end - trampoline_start,%ecx > >> > rep movsb > >> > > >> > >> The latest at this final hunk I'm getting tired (and upset). I'd much > >> rather not touch all this code in these fragile ways, and instead > >> require Xen to be booted without grub2 on badly written firmware > >> like the one on the machine you quote in the description. > > > > Let's start discussion from here. My further work on this patch series > > is pointless until we do not agree details in this case. > > > > So, I agree that any software (including firmware) should not use > > precious resources (i.e. low memory in that case) if it is not strictly > > required. And I do not think so that latest UEFI implementations > > on new hardware really need this low memory to survive (at least page > > tables could be put anywhere above low memory). However, in case of > > UEFI it is a wish of smart people not requirement set by spec. I was > > checking UEFI docs a few times but I was not able to find anything > > which says that e.g. "...developer MUST allocate memory outside of low > > memory ...". Even I have not found any suggestion about that. However, > > I must admit that I do not know whole UEFI spec, so, if you know > something > > which is similar to above please tell me where it is (title, revision, > > page, paragraph, etc.). Hence, if there is not strict requirement in > > regards to memory allocation in specs we are lost. Of course we can > > encourage people to not do nasty things but I do not believe that many > > will listen. So, sadly, I suppose that we will see more and more machines > > in the wild which are "broken" (well, let's say do not align to good > > practices). > > > > On the other hand I think that we should not assume that a given memory > > region (in our case starting at 1 MiB) is (or will be) available in every > > machine. I have not seen anything which says that it is true. We should > > stop doing that even if it works right now. I think that it works by > > chance and there is a chance that it will stop working one day because > > somebody will discover that he or she can put there e.g. device or hole. > > > > Last but not least. I suppose that Xen users and especially distros will > > complain when they are not able to use GRUB2 with Xen on every platform > > just because somebody (i.e. platform designers, developers, or whatever) > > do not accept our beliefs or we require that platform must obey rules > > (i.e. memory map requirements) which are specified nowhere. > > You're right, there's no such requirement on memory use in the spec. > But you're missing the point. Supporting grub2 on UEFI is already a > hack (ignoring all intentions EFI had from its first days). And now > you've found an environment where that hack needs another hack > (in Xen) to actually work. That's too much hackery for my taste, the > more that things on this system can (afaict) work quite okay (without > grub2, or with using its chainloader mechanism). > > If you advocate direct booting ( no boot loader) on production machines I wont argue much, as long as there is good recovery tools to deal with failed boots (grub does this very well, I am not aware of anything comparable that is pure efi). however the other use case which care more about is dual booting. I am a novice when it comes to Xen, although otherwise competent. The test machines I have for playing with Xen are also used for other tests, some of which require raw hardware support, so I want the ability to use a boot menu. I am aware of refit, but it does not have serial support which makes automating testing more difficult. and I have not yet got ipxe to successfully boot Xen (although this is purely because I have not yet devoted enough time to that project and I am not yet familiar with how Xen boots). So no, I'm still not convinced of the need for this patch. > I am at a loss for alternatives. Yes grub on efi violates the spirit of efi. Propose a better way forward rather than deriding those who have found a successful, portable way around the limitations of efi implementations. > > Jan > > > _______________________________________________ > Grub-devel mailing list > Grub-devel@gnu.org > https://lists.gnu.org/mailman/listinfo/grub-devel > -- -- Ben Hildred Automation Support Services 303 815 6721
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