linux-kernel - Re: [PATCH RFC] usercopy: optimize stack check flow when the

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Date:   Tue, 14 Aug 2018 05:34:54 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Xiaofeng Yuan <yuanxiaofeng1@...wei.com>
Cc:     keescook@...omium.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] usercopy: optimize stack check flow when the

On Tue, Aug 14, 2018 at 08:17:31PM +0800, Xiaofeng Yuan wrote:
> The check_heap_object() checks the spanning multiple pages and slab.
> When the page-spanning test is disabled, the check_heap_object() is
> redundant for spanning multiple pages. However, the kernel stacks are
> multiple pages under certain conditions: CONFIG_ARCH_THREAD_STACK_ALLOCATOR
> is not defined and (THREAD_SIZE >= PAGE_SIZE). At this point, We can skip
> the check_heap_object() for kernel stacks to improve performance.
> Similarly, the virtually-mapped stack can skip check_heap_object() also,
> beacause virt_addr_valid() will return.

Why not just check_stack_object() first, then check_heap_object() second?