linux-kernel - Re: [PATCH 3/4] tee: Remove call to get_kernel

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Message-ID: <YzjfcW6OGcPP075q@ZenIV>
Date:   Sun, 2 Oct 2022 01:46:41 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     ira.weiny@...el.com
Cc:     Jens Wiklander <jens.wiklander@...aro.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        op-tee@...ts.trustedfirmware.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 3/4] tee: Remove call to get_kernel_pages()

On Sat, Oct 01, 2022 at 05:23:25PM -0700, ira.weiny@...el.com wrote:

>  	kiov = kcalloc(page_count, sizeof(*kiov), GFP_KERNEL);
> @@ -38,12 +39,12 @@ static int shm_get_kernel_pages(unsigned long start, size_t page_count,
>  	for (n = 0; n < page_count; n++) {
>  		kiov[n].iov_base = (void *)(start + n * PAGE_SIZE);
>  		kiov[n].iov_len = PAGE_SIZE;
> +		pages[n] = virt_to_page(kiov[n].iov_base);
> +		get_page(pages[n]);
>  	}
> -
> -	rc = get_kernel_pages(kiov, page_count, 0, pages);
>  	kfree(kiov);

IDGI.  The only thing in kiov[...] you are every reading is
->iov_base.  And you fetch it once, right after the assignment.

Why bother with allocating the array at all?
		pages[n] = virt_to_page((void *)start + n * PAGE_SIZE);
would do just as well, not to mention the fact that since you reject
vmalloc and kmap, you might simply do

	page = virt_to_page(start);
	for (int n = 0; n < page_count; n++)
		get_page(pages[n] = page + n);

instead...