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Re: [RFC PATCH 01/28] x86/pvh: Call C code via the kernel virtual mapping
- To: Ard Biesheuvel <ardb+git@xxxxxxxxxx>, <linux-kernel@xxxxxxxxxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Wed, 25 Sep 2024 17:12:51 -0400
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- Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>, <x86@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Uros Bizjak <ubizjak@xxxxxxxxx>, Dennis Zhou <dennis@xxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>, "Paolo Bonzini" <pbonzini@xxxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Masahiro Yamada <masahiroy@xxxxxxxxxx>, Kees Cook <kees@xxxxxxxxxx>, Nathan Chancellor <nathan@xxxxxxxxxx>, Keith Packard <keithp@xxxxxxxxxx>, Justin Stitt <justinstitt@xxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, "Arnaldo Carvalho de Melo" <acme@xxxxxxxxxx>, Namhyung Kim <namhyung@xxxxxxxxxx>, "Jiri Olsa" <jolsa@xxxxxxxxxx>, Ian Rogers <irogers@xxxxxxxxxx>, Adrian Hunter <adrian.hunter@xxxxxxxxx>, Kan Liang <kan.liang@xxxxxxxxxxxxxxx>, <linux-doc@xxxxxxxxxxxxxxx>, <linux-pm@xxxxxxxxxxxxxxx>, <kvm@xxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>, <linux-efi@xxxxxxxxxxxxxxx>, <linux-arch@xxxxxxxxxxxxxxx>, <linux-sparse@xxxxxxxxxxxxxxx>, <linux-kbuild@xxxxxxxxxxxxxxx>, <linux-perf-users@xxxxxxxxxxxxxxx>, <rust-for-linux@xxxxxxxxxxxxxxx>, <llvm@xxxxxxxxxxxxxxx>
- Delivery-date: Wed, 25 Sep 2024 21:13:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2024-09-25 11:01, Ard Biesheuvel wrote:
From: Ard Biesheuvel <ardb@xxxxxxxxxx>
Calling C code via a different mapping than it was linked at is
problematic, because the compiler assumes that RIP-relative and absolute
symbol references are interchangeable. GCC in particular may use
RIP-relative per-CPU variable references even when not using -fpic.
So call xen_prepare_pvh() via its kernel virtual mapping on x86_64, so
that those RIP-relative references produce the correct values. This
matches the pre-existing behavior for i386, which also invokes
xen_prepare_pvh() via the kernel virtual mapping before invoking
startup_32 with paging disabled again.
Fixes: 7243b93345f7 ("xen/pvh: Bootstrap PVH guest")
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Tested-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
I found that before this change xen_prepare_pvh() would call through
some pv_ops function pointers into the kernel virtual mapping.
Regards,
Jason
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