Re: [Xen-devel] [PATCH v3 06/18] livepatch: Initial ARM64 support.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.09.16 at 22:35, <konrad.wilk@xxxxxxxxxx> wrote:
> As compared to x86 the va of the hypervisor .text
> is locked down - we cannot modify the running pagetables
> to have the .ro flag unset. We borrow the same idea that
> alternative patching has - which is to vmap the entire
> .text region and use the alternative virtual address
> for patching.
> 
> Since we are doing vmap we may fail, hence the
> arch_livepatch_quiesce was changed (see "x86,arm:
> Change arch_livepatch_quiesce() declaration") to return
> an error value which will be bubbled in payload->rc and
> provided to the user (along with messages in the ring buffer).
> 
> The livepatch virtual address space (where the new functions
> are) needs to be close to the hypervisor virtual address
> so that the trampoline can reach it. As such we re-use
> the BOOT_RELOC_VIRT_START which is not used after bootup
> (alternatively we can also use the space after the _end to
> FIXMAP_ADDR(0), but that may be too small).
> 
> The ELF relocation engine at the start was coded from
> the "ELF for the ARM 64-bit Architecture (AArch64)"
> (http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056b/IHI0056B_aaelf64.
> pdf)
> but after a while of trying to write the correct bit shifting
> and masking from scratch I ended up borrowing from Linux, the
> 'reloc_insn_imm' (Linux v4.7 arch/arm64/kernel/module.c function.
> See 257cb251925f854da435cbf79b140984413871ac "arm64: Loadable modules")
> 
> And while at it - we also utilize code from Linux to construct
> the right branch instruction (see "arm64/insn: introduce
> aarch64_insn_gen_{nop|branch_imm}() helper functions").
> 
> In the livepatch payload loading code we tweak the #ifdef to
> only exclude ARM_32. The exceptions are not part of ARM 32/64 hence
> they are still behind the #ifdef.
> 
> We also expand the MAINTAINERS file to include the arm64 and arm32
> platform specific livepatch file.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> ---
> Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc  Jan Beulich <jbeulich@xxxxxxxx>

Oops.

Non-ARM parts:
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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