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

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Message-ID: <daf28e5b-61ba-42ff-97ba-aaaeaac81c09@suse.com>
Date: Mon, 16 Sep 2024 08:33:34 +0200
From: Juergen Gross <jgross@...e.com>
To: Jason Andryuk <jason.andryuk@....com>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 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>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Brian Gerst <brgerst@...il.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/5] x86/pvh: Add 64bit relocation page tables

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@....com>

Reviewed-by: Juergen Gross <jgross@...e.com>

Juergen

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