linux-kernel - Re: [PATCH v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or the clear info about PTEs

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Message-ID: <af55d3d8-31d8-0deb-d76f-b6d464ad7262@collabora.com>
Date:   Tue, 21 Feb 2023 12:02:17 +0500
From:   Muhammad Usama Anjum <usama.anjum@...labora.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Muhammad Usama Anjum <usama.anjum@...labora.com>,
        Peter Xu <peterx@...hat.com>,
        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>,
        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>,
        Nadav Amit <namit@...are.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 v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or
 the clear info about PTEs

On 2/20/23 6:26 PM, Mike Rapoport wrote:
> Hi,
> 
> On Thu, Feb 02, 2023 at 04:29:12PM +0500, Muhammad Usama Anjum wrote:
>> This IOCTL, PAGEMAP_SCAN on pagemap file can be used to get and/or clear
>> the info about page table entries. The following operations are supported
>> in this ioctl:
>> - Get the information if the pages have been written-to (PAGE_IS_WRITTEN),
>>   file mapped (PAGE_IS_FILE), present (PAGE_IS_PRESENT) or swapped
>>   (PAGE_IS_SWAPPED).
>> - Write-protect the pages (PAGEMAP_WP_ENGAGE) to start finding which
>>   pages have been written-to.
>> - Find pages which have been written-to and write protect the pages
>>   (atomic PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE)
>>
>> +/*
>> + * struct pagemap_scan_arg - Pagemap ioctl argument
>> + * @start:		Starting address of the region
>> + * @len:		Length of the region (All the pages in this length are included)
>> + * @vec:		Address of page_region struct array for output
>> + * @vec_len:		Length of the page_region struct array
>> + * @max_pages:		Optional max return pages
>> + * @flags:		Flags for the IOCTL
>> + * @required_mask:	Required mask - All of these bits have to be set in the PTE
>> + * @anyof_mask:		Any mask - Any of these bits are set in the PTE
>> + * @excluded_mask:	Exclude mask - None of these bits are set in the PTE
>> + * @return_mask:	Bits that are to be reported in page_region
>> + */
>> +struct pagemap_scan_arg {
>> +	__u64 start;
>> +	__u64 len;
>> +	__u64 vec;
>> +	__u64 vec_len;
>> +	__u32 max_pages;
>> +	__u32 flags;
>> +	__u64 required_mask;
>> +	__u64 anyof_mask;
>> +	__u64 excluded_mask;
>> +	__u64 return_mask;
>> +};
> 
> After Nadav's comment I've realized I missed the API part :)
> 
> A few quick notes for now:
> * The arg struct is fixed, so it would be impossible to extend the API
> later. Following the clone3() example, I'd add 'size' field to the
> pagemam_scan_arg so that it would be possible to add new fields afterwards.
> * Please make flags __u64, just in case
> * Put size and flags at the beginning of the struct, e.g.
> 
> strucr pagemap_scan_arg {
> 	size_t size;
> 	__u64 flags;
> 	/* all the rest */
> };
Updated. Thank you so much!

> 
>> +
>> +/* Special flags */
>> +#define PAGEMAP_WP_ENGAGE	(1 << 0)
>> +
>>  #endif /* _UAPI_LINUX_FS_H */
>> -- 
>> 2.30.2
>>
> 

-- 
BR,
Muhammad Usama Anjum