Re: [Xen-devel] [PATCH v3 11/17] livepatch/x86/arm[32, 64]: Use common vmap code for applying.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/09/17 01:37, Konrad Rzeszutek Wilk wrote:
> Patch titled "livepatch/arm[32,64]: Modify livepatch_funcs" added
> the infrastructure on ARM [32,64] to use vmap as way to
> map read-only regions. On x86 we use a global register.
>
> But there is nothing wrong with using on x86 the same method
> as on ARM[32,64] - which is exactly what this patch does.

Yes there is :)

If you don't make updates to the .text section via the same linear
address as the instructions are being fetched, the Icache doesn't stay
synchronised.  This is VeryBad(tm) when patching the entry paths.

If you want to continue down this route, you need to reintroduce
sync_core() and call it appropriately on all cpus after patching is
complete, and take care to ensure that any spliced patch on the NMI/MCE
handlers still results in valid x86 opcode.

~Andrew

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