Re: [tip:perf/urgent] uprobes: Fix uprobes on MIPS, allow for a cache flush after ixol breakpoint creation

[Oleg Nesterov]

On 12/19, tip-bot for Marcin Nowakowski wrote:
>
> uprobes: Fix uprobes on MIPS, allow for a cache flush after ixol breakpoint creation
>
> Commit:
>
>   72e6ae285a1d ('ARM: 8043/1: uprobes need icache flush after xol write'
>
> ... has introduced an arch-specific method to ensure all caches are
> flushed appropriately after an instruction is written to an XOL page.

when this page is already mmaped,

> However, when the XOL area is created and the out-of-line breakpoint
> instruction is copied, caches are not flushed at all and stale data may
> be found in icache.

but in this case the page is not mmaped yet, the probed application will
take a page fault if it tries to execute this insn,

> Replace a simple copy_to_page() with arch_uprobe_copy_ixol() to allow
> the arch to ensure all caches are updated accordingly.
>
> This change fixes uprobes on MIPS InterAptiv (tested on Creator Ci40).

OK, I know nothing about MIPS, but could you help me understand this change?

See above. If we really need flush_icache_range() here then perhaps we should
modify install_special_mapping() and/or __do_fault/special_mapping_fault paths
instead?

Oleg.