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From: Thomas Gleixner <tglx@linutronix.de>
To: Pasha Tatashin <pasha.tatashin@soleen.com>, Andy Lutomirski
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Subject: Re: [RFC 11/14] x86: add support for Dynamic Kernel Stacks
In-Reply-To: <CA+CK2bA22AP2jrbHjdN8nYFbYX2xJXQt+=4G3Rjw_Lyn5NOyKA@mail.gmail.com>
References: <20240311164638.2015063-1-pasha.tatashin@soleen.com>
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Date: Tue, 12 Mar 2024 00:33:58 +0100
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On Mon, Mar 11 2024 at 19:10, Pasha Tatashin wrote:
> On Mon, Mar 11, 2024 at 6:17=E2=80=AFPM Andy Lutomirski <luto@kernel.org>=
 wrote:
>> Also, I think the whole memory allocation concept in this whole
>> series is a bit odd.  Fundamentally, we *can't* block on these stack
>> faults -- we may be in a context where blocking will deadlock.  We
>> may be in the page allocator.  Panicing due to kernel stack
>> allocation would be very unpleasant.
>
> We never block during handling stack faults. There's a per-CPU page
> pool, guaranteeing availability for the faulting thread. The thread
> simply takes pages from this per-CPU data structure and refills the
> pool when leaving the CPU. The faulting routine is efficient,
> requiring a fixed number of loads without any locks, stalling, or even
> cmpxchg operations.

Is this true for any context including nested exceptions and #NMI?

Thanks,

        tglx