linux-kernel - Re: [RFC 00/14] Dynamic Kernel Stacks

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Date: Mon, 18 Mar 2024 15:19:50 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: David Laight <David.Laight@...lab.com>,
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Subject: Re: [RFC 00/14] Dynamic Kernel Stacks

On Mon, Mar 18, 2024 at 11:09:47AM -0400, Pasha Tatashin wrote:
> The TLB load is going to be exactly the same as today, we already use
> small pages for VMA mapped stacks. We won't need to have extra
> flushing either, the mappings are in the kernel space, and once pages
> are removed from the page table, no one is going to access that VA
> space until that thread enters the kernel again. We will need to
> invalidate the VA range only when the pages are mapped, and only on
> the local cpu.

No; we can pass pointers to our kernel stack to other threads.  The
obvious one is a mutex; we put a mutex_waiter on our own stack and
add its list_head to the mutex's waiter list.  I'm sure you can
think of many other places we do this (eg wait queues, poll(), select(),
etc).