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Re: [RFC PATCH 06/28] x86/percpu: Get rid of absolute per-CPU variable placement
- To: Ard Biesheuvel <ardb+git@xxxxxxxxxx>
- From: "Christoph Lameter (Ampere)" <cl@xxxxxxxxxx>
- Date: Wed, 25 Sep 2024 10:56:38 -0700 (PDT)
- Cc: linux-kernel@xxxxxxxxxxxxxxx, 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>, 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 18:29:06 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, 25 Sep 2024, Ard Biesheuvel wrote:
> The x86_64 approach was needed to accommodate per-task stack protector
> cookies, which used to live at a fixed offset of GS+40, requiring GS to
> be treated as a base register. This is no longer the case, though, and
> so GS can be repurposed as a true per-CPU offset, adopting the same
> strategy as other architectures.
>
> This also removes the need for linker tricks to emit the per-CPU ELF
> segment at a different virtual address. It also means RIP-relative
> per-CPU variables no longer need to be relocated in the opposite
> direction when KASLR is applied, which was necessary because the 0x0
> based per-CPU region remains in place even when the kernel is moved
> around.
Looks like a good cleanup. Hope it does not break anything that relies on
structures %GS points to.
Reviewed-by: Christoph Lameter <cl@xxxxxxxxx>
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