[PATCH] powerpc/xmon: Lower limits on nidump and ndump

[Michael Ellerman]

On Wed, 2020-02-19 at 11:00:07 UTC, Michael Ellerman wrote:
> In xmon we have two variables that are used by the dump commands.
> There's ndump which is the number of bytes to dump using 'd', and
> nidump which is the number of instructions to dump using 'di'.
> 
> ndump starts as 64 and nidump starts as 16, but both can be set by the
> user.
> 
> It's fairly common to be pasting addresses into xmon when trying to
> debug something, and if you inadvertently double paste an address like
> so:
> 
>   0:mon> di c000000002101f6c c000000002101f6c
> 
> The second value is interpreted as the number of instructions to dump.
> 
> Luckily it doesn't dump 13 quintrillion instructions, the value is
> limited to MAX_DUMP (128K). But as each instruction is dumped on a
> single line, that's still a lot of output. If you're on a slow console
> that can take multiple minutes to print. If you were "just popping in
> and out of xmon quickly before the RCU/hardlockup detector fires" you
> are now having a bad day.
> 
> Things are not as bad with 'd' because we print 16 bytes per line, so
> it's fewer lines. But it's still quite a lot.
> 
> So shrink the maximum for 'd' to 64K (one page), which is 4096 lines.
> For 'di' add a new limit which is the above / 4 - because instructions
> are 4 bytes, meaning again we can dump one page.
> 
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/d64c7dbb4d98306b794401ca924ad053f84b59f8

cheers