linux-kernel - Re: [PATCH v13 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

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Message-ID: <ZD2hCoTqSMtpjmaX@x1n>
Date:   Mon, 17 Apr 2023 15:42:02 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <emmir@...gle.com>,
        Andrei Vagin <avagin@...il.com>,
        Danylo Mocherniuk <mdanylo@...gle.com>,
        Paul Gofman <pgofman@...eweavers.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Yang Shi <shy828301@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Yun Zhou <yun.zhou@...driver.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Alex Sierra <alex.sierra@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Greg KH <gregkh@...uxfoundation.org>, kernel@...labora.com
Subject: Re: [PATCH v13 2/5] fs/proc/task_mmu: Implement IOCTL to get and
 optionally clear info about PTEs

Muhammad,

On Mon, Apr 17, 2023 at 05:56:27PM +0500, Muhammad Usama Anjum wrote:
> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
> +				  unsigned long end, struct mm_walk *walk)
> +{
> +	struct pagemap_scan_private *p = walk->private;
> +	struct vm_area_struct *vma = walk->vma;
> +	unsigned long addr = end;
> +	pte_t *pte, *orig_pte;
> +	spinlock_t *ptl;
> +	bool is_written;
> +	int ret = 0;
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	ptl = pmd_trans_huge_lock(pmd, vma);
> +	if (ptl) {
> +		unsigned long n_pages = (end - start)/PAGE_SIZE;
> +
> +		if (p->max_pages && n_pages > p->max_pages - p->found_pages)
> +			n_pages = p->max_pages - p->found_pages;
> +
> +		is_written = !is_pmd_uffd_wp(*pmd);
> +
> +		/*
> +		 * Break huge page into small pages if the WP operation need to
> +		 * be performed is on a portion of the huge page.
> +		 */
> +		if (is_written && PM_SCAN_DO_UFFD_WP(p) &&
> +		    n_pages < HPAGE_SIZE/PAGE_SIZE) {
> +			spin_unlock(ptl);
> +			split_huge_pmd(vma, pmd, start);
> +			goto process_smaller_pages;
> +		}
> +
> +		ret = pagemap_scan_output(is_written, vma->vm_file,
> +					  pmd_present(*pmd), is_swap_pmd(*pmd),
> +					  p, start, n_pages);
> +
> +		if (ret >= 0 && is_written && PM_SCAN_DO_UFFD_WP(p))
> +			make_uffd_wp_pmd(vma, addr, pmd);
> +
> +		spin_unlock(ptl);
> +		return ret;
> +	}
> +process_smaller_pages:
> +	if (pmd_trans_unstable(pmd))
> +		return 0;
> +#endif
> +
> +	pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
> +	for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {
> +		is_written = !is_pte_uffd_wp(*pte);
> +
> +		ret = pagemap_scan_output(is_written, vma->vm_file,
> +					  pte_present(*pte), is_swap_pte(*pte),
> +					  p, addr, 1);
> +
> +		if (ret >= 0 && is_written && PM_SCAN_DO_UFFD_WP(p))
> +			make_uffd_wp_pte(vma, addr, pte);
> +	}
> +	pte_unmap_unlock(orig_pte, ptl);

IIUC tlb flushes, mmu notifications are still missing here, am I right?

Thanks,

> +
> +	cond_resched();
> +	return ret;
> +}

-- 
Peter Xu