On Sun, 2015-09-20 at 20:15 +0200, Andreas Sundstrom wrote: > On 2015-09-20 18:51, Ian Campbell wrote: > > On Sat, 2015-09-19 at 18:49 +0200, Andreas Sundstrom wrote: > > > Package: grub-xen-host > > > Version: 2.02~beta2-22 > > > Severity: important > > > > > > Dear Maintainer, > > > > > > Using 64-bit dom0 and 32-bit domU PV (para-virtualized) grub > > > sometimes > > > fail when chainloading the domU's grub. 64-bit domU seem to work 100% > > > of the time. > > Which grub are you starting with from dom0? > > > > If you want to boot a 32-bit guest (which includes chainloading a 32 > > -bit grub) then you must start with the 32-bit grub-i386-xen.bin grub > > binary to create a 32-bit guest. > > > > kexecing from 64-bit to 32-bit is not possible in the general case. In > > fact I thought it was _impossible_ in all cases and would have ruled it > > out as something you might be doing, except some of these registers > > look like 64-bit values: > > As you say it has not been possible at any time to use 64-bit grub from > dom0 and then load either 32-bit grub or linux kernel from domU. > > I am using /usr/lib/grub-xen/grub-i386-xen.bin when I start my i386 > domU's
OK good (well, bad, because now I have no idea what is going wrong...) > Thanks for your great blog entry about this by the way: > https://blog.xenproject.org/2015/01/07/using-grub-2-as-a-bootloader-for-x > en-pv-guests/ > I have used it to get a better understanding of the whole process. > > > (XEN) rax: 0000000000000000 rbx: 0000000000000000 rcx: > > 0000000000000000 > > > (XEN) rdx: 0000000000000000 rsi: 0000000000499000 rdi: > > > 0000000000800000 > > > (XEN) rbp: 000000000000000a rsp: 00000000005a5ff0 r8: > > > 0000000000000000 > > > (XEN) r9: 0000000000000000 r10: ffff83023e9b9000 r11: > > > ffff83023e9b9000 > > > (XEN) r12: 0000033f3d335bfb r13: ffff82d080300800 r14: > > > ffff82d0802ea940 > > > (XEN) r15: ffff83005e819000 cr0: 000000008005003b cr4: > > > 00000000000506f0 > > > (XEN) cr3: 0000000200b7a000 cr2: 0000000000000000 > Well I don't know but I guess the XEN hypervisor is always running in > 64-bit mode yes? > I suppose that maybe even if the domU is 32-bit any errors showing up in > "xl dmesg" > reflects the mode that the hypervisor is run in? I think it's supposed to reflect the mode which the processor is in at the time. I trimmed the quotes but there was a line in the dump which said: (XEN) RFLAGS: 0000000000000246 EM: 1 CONTEXT: pv guest Suggesting that this was guest context (this string doesn't distinguish 32- from 64-bit). Actually, I just spotted: (XEN) domain_crash_sync called from entry.S: fault at ffff82d08021feb0 compat_create_bounce_frame+0xc6/0xde where compat == 32-bit, so that bit is correct. So I think the large register values are a red-herring. I think it would be worth reporting this to upstream (both Xen and Grub), would you mind doing so? Ian.
