On Thu, Mar 14, 2024 at 12:59:19PM -0400, Jason Andryuk wrote: > On 2024-03-14 11:30, Jan Beulich wrote: > > On 14.03.2024 15:33, Roger Pau Monné wrote: > > > On Thu, Mar 14, 2024 at 09:51:22AM -0400, Jason Andryuk wrote: > > > > On 2024-03-14 05:48, Roger Pau Monné wrote: > > > > > On Wed, Mar 13, 2024 at 03:30:21PM -0400, Jason Andryuk wrote: > > > > > > @@ -234,6 +235,17 @@ elf_errorstatus elf_xen_parse_note(struct > > > > > > elf_binary *elf, > > > > > > elf_note_numeric_array(elf, note, 8, 0), > > > > > > elf_note_numeric_array(elf, note, 8, 1)); > > > > > > break; > > > > > > + > > > > > > + case XEN_ELFNOTE_PVH_RELOCATION: > > > > > > + if ( elf_uval(elf, note, descsz) != 3 * sizeof(uint64_t) ) > > > > > > + return -1; > > > > > > + > > > > > > + parms->phys_min = elf_note_numeric_array(elf, note, 8, 0); > > > > > > + parms->phys_max = elf_note_numeric_array(elf, note, 8, 1); > > > > > > + parms->phys_align = elf_note_numeric_array(elf, note, 8, > > > > > > 2); > > > > > > > > > > Size for those needs to be 4 (32bits) as the entry point is in 32bit > > > > > mode? I don't see how we can start past the 4GB boundary. > > > > > > > > I specified the note as 3x 64bit values. It seemed simpler than trying > > > > to > > > > support both 32bit and 64bit depending on the kernel arch. Also, just > > > > using > > > > 64bit provides room in case it is needed in the future. > > > > > > Why do you say depending on the kernel arch? > > > > > > PVH doesn't know the bitness of the kernel, as the kernel entry point > > > is always started in protected 32bit mode. We should just support > > > 32bit values, regardless of the kernel bitness, because that's the > > > only range that's suitable in order to jump into the entry point. > > > > > > Note how XEN_ELFNOTE_PHYS32_ENTRY is also unconditionally a 32bit > > > integer. > > Linux defines PHYS32_ENTRY with _ASM_PTR, so it's 32 or 64 bit to match how > the kernel is compiled. The Xen code parses the integer according to the > size of the note.
I think that's wrong, PHYS32_ENTRY should strictly be a 32bit integer, in fact the field in struct elf_dom_parms is an uint32_t, so Linux using _ASM_PTR seems bogus, it should unconditionally use .long regardless of the kernel bitness. > > > > Do you want the note to be changed to 3x 32bit values? > > > > > > Unless anyone objects, yes, that's would be my preference. > > > > As mentioned elsewhere, unless the entire note is meant to be x86-specific, > > this fixed-32-bit property then would want limiting to x86. > > PVH is only implemented for x86 today. Are you saying that the comment > should just specify the values are 32bit for x86? If the note is reused for > other arches, then they can specify their usage? > > If this note is to be a variably sized array of values, then the elements > should be of fixed size. Otherwise parsing is ambiguous without, say, > another field specifying element size. > > Maybe XEN_ELFNOTE_PHYS32_RELOC would be a better name to complement the > PHYS32_ENTRY? IMO the '32' part of PHYS32_ENTRY is kind of redundant, given the CPU state when using such entry point it's impossible to use 64bit addresses. I would be fine with using XEN_ELFNOTE_PHYS_RELOC or some such. Anyway, this is just a name so I'm not going to opposed if Jan and yourself prefer to keep using PHYS32. Thanks, Roger.
