Message-ID: <f8cf8e13-cbd3-4dfa-b09c-e0a14f0e346c@suse.com>
Date: Mon, 16 Sep 2024 10:44:52 +0200
From: Juergen Gross <jgross@...e.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
 Jason Andryuk <jason.andryuk@....com>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Brian Gerst <brgerst@...il.com>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH v3 0/5] x86/pvh: Make 64bit PVH entry relocatable

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


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