Using the PVH entry point, the uncompressed vmlinux is loaded at
LOAD_PHYSICAL_ADDR, and execution starts in 32bit mode at the
address in XEN_ELFNOTE_PHYS32_ENTRY, pvh_start_xen, with paging
disabled.

Loading at LOAD_PHYSICAL_ADDR has not been a problem in the past as
virtual machines don't have conflicting memory maps.  But Xen now
supports a PVH dom0, which uses the host memory map, and there are
Coreboot/EDK2 firmwares that have reserved regions conflicting with
LOAD_PHYSICAL_ADDR.  Xen recently added XEN_ELFNOTE_PHYS32_RELOC to
specify an alignment, minimum and maximum load address when
LOAD_PHYSICAL_ADDR cannot be used.  This patch series makes the PVH
entry path PIC to support relocation.

Only x86-64 is converted.  The 32bit entry path calling into vmlinux,
which is not PIC, will not support relocation.

The entry path needs pages tables to switch to 64bit mode.  A new
pvh_init_top_pgt is added to make the transition into the startup_64
when the regular init_top_pgt pagetables are setup.  This duplication is
unfortunate, but it keeps the changes simpler.  __startup_64() can't be
used to setup init_top_pgt for PVH entry because it is 64bit code - the
32bit entry code doesn't have page tables to use.

This is the straight forward implementation to make it work.  Other
approaches could be pursued.

checkpatch.pl gives an error: "ERROR: Macros with multiple statements
should be enclosed in a do - while loop" about the moved PMDS macro.
But PMDS is an assembler macro, so its not applicable.  There are some
false positive warnings "WARNING: space prohibited between function name
and open parenthesis '('" about the macro, too.

v2 addresses review feedback.  It also replace LOAD_PHYSICAL_ADDR with
_pa(pvh_start_xen) in some offset calculations.  They happened to be
equal in my original builds.  When the two values differ,
_pa(pvh_start_xen) is the correct one to use.

v3: Fix build error for 32bit.  Add Juergen's R-b to patch 4.

Jason Andryuk (5):
  xen: sync elfnote.h from xen tree
  x86/pvh: Make PVH entrypoint PIC for x86-64
  x86/pvh: Set phys_base when calling xen_prepare_pvh()
  x86/kernel: Move page table macros to header
  x86/pvh: Add 64bit relocation page tables

 arch/x86/include/asm/pgtable_64.h |  23 ++++-
 arch/x86/kernel/head_64.S         |  20 ----
 arch/x86/platform/pvh/head.S      | 161 +++++++++++++++++++++++++++---
 include/xen/interface/elfnote.h   |  93 ++++++++++++++++-
 4 files changed, 259 insertions(+), 38 deletions(-)


base-commit: 7c626ce4bae1ac14f60076d00eafe71af30450ba
-- 
2.34.1

x86 maintainers,

are you going to pick this series up, or should I take it via the
Xen tree?


Juergen

On 23.08.24 21:36, Jason Andryuk wrote:
> Using the PVH entry point, the uncompressed vmlinux is loaded at
> LOAD_PHYSICAL_ADDR, and execution starts in 32bit mode at the
> address in XEN_ELFNOTE_PHYS32_ENTRY, pvh_start_xen, with paging
> disabled.
> 
> Loading at LOAD_PHYSICAL_ADDR has not been a problem in the past as
> virtual machines don't have conflicting memory maps.  But Xen now
> supports a PVH dom0, which uses the host memory map, and there are
> Coreboot/EDK2 firmwares that have reserved regions conflicting with
> LOAD_PHYSICAL_ADDR.  Xen recently added XEN_ELFNOTE_PHYS32_RELOC to
> specify an alignment, minimum and maximum load address when
> LOAD_PHYSICAL_ADDR cannot be used.  This patch series makes the PVH
> entry path PIC to support relocation.
> 
> Only x86-64 is converted.  The 32bit entry path calling into vmlinux,
> which is not PIC, will not support relocation.
> 
> The entry path needs pages tables to switch to 64bit mode.  A new
> pvh_init_top_pgt is added to make the transition into the startup_64
> when the regular init_top_pgt pagetables are setup.  This duplication is
> unfortunate, but it keeps the changes simpler.  __startup_64() can't be
> used to setup init_top_pgt for PVH entry because it is 64bit code - the
> 32bit entry code doesn't have page tables to use.
> 
> This is the straight forward implementation to make it work.  Other
> approaches could be pursued.
> 
> checkpatch.pl gives an error: "ERROR: Macros with multiple statements
> should be enclosed in a do - while loop" about the moved PMDS macro.
> But PMDS is an assembler macro, so its not applicable.  There are some
> false positive warnings "WARNING: space prohibited between function name
> and open parenthesis '('" about the macro, too.
> 
> v2 addresses review feedback.  It also replace LOAD_PHYSICAL_ADDR with
> _pa(pvh_start_xen) in some offset calculations.  They happened to be
> equal in my original builds.  When the two values differ,
> _pa(pvh_start_xen) is the correct one to use.
> 
> v3: Fix build error for 32bit.  Add Juergen's R-b to patch 4.
> 
> Jason Andryuk (5):
>    xen: sync elfnote.h from xen tree
>    x86/pvh: Make PVH entrypoint PIC for x86-64
>    x86/pvh: Set phys_base when calling xen_prepare_pvh()
>    x86/kernel: Move page table macros to header
>    x86/pvh: Add 64bit relocation page tables
> 
>   arch/x86/include/asm/pgtable_64.h |  23 ++++-
>   arch/x86/kernel/head_64.S         |  20 ----
>   arch/x86/platform/pvh/head.S      | 161 +++++++++++++++++++++++++++---
>   include/xen/interface/elfnote.h   |  93 ++++++++++++++++-
>   4 files changed, 259 insertions(+), 38 deletions(-)
> 
> 
> base-commit: 7c626ce4bae1ac14f60076d00eafe71af30450ba

On 16.09.24 10:44, Juergen Gross wrote:
> x86 maintainers,
> 
> are you going to pick this series up, or should I take it via the
> Xen tree?

I take the silence as a "its okay to go via the Xen tree".


Juergen

On 9/25/24 02:28, Juergen Gross wrote:
> On 16.09.24 10:44, Juergen Gross wrote:
>> x86 maintainers,
>>
>> are you going to pick this series up, or should I take it via the
>> Xen tree?
> 
> I take the silence as a "its okay to go via the Xen tree".

Or, "most of us were traveling last week and in a bigger email hole than
normal". ;)

But, yeah, feel free to take this via the Xen tree.  I just acked the
only one that's not quite Xen-specific.