Re: [PATCH v3 5/5] x86/pvh: Add 64bit relocation page tables

[Juergen Gross <jgross@xxxxxxxx>]

On 23.08.24 21:36, Jason Andryuk wrote:
> The PVH entry point is 32bit.  For a 64bit kernel, the entry point must
> switch to 64bit mode, which requires a set of page tables.  In the past,
> PVH used init_top_pgt.
>
> This works fine when the kernel is loaded at LOAD_PHYSICAL_ADDR, as the
> page tables are prebuilt for this address.  If the kernel is loaded at a
> different address, they need to be adjusted.
>
> __startup_64() adjusts the prebuilt page tables for the physical load
> address, but it is 64bit code.  The 32bit PVH entry code can't call it
> to adjust the page tables, so it can't readily be re-used.
>
> 64bit PVH entry needs page tables set up for identity map, the kernel
> high map and the direct map.  pvh_start_xen() enters identity mapped.
> Inside xen_prepare_pvh(), it jumps through a pv_ops function pointer
> into the highmap.  The direct map is used for __va() on the initramfs
> and other guest physical addresses.
>
> Add a dedicated set of prebuild page tables for PVH entry.  They are
> adjusted in assembly before loading.
>
> Add XEN_ELFNOTE_PHYS32_RELOC to indicate support for relocation
> along with the kernel's loading constraints.  The maximum load address,
> KERNEL_IMAGE_SIZE - 1, is determined by a single pvh_level2_ident_pgt
> page.  It could be larger with more pages.
>
> Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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