Re: [PATCH v7 3/4] fs/proc/task_mmu: Implement IOCTL to get and/or the clear info about PTEs

From: Muhammad Usama Anjum <usama.anjum@collabora.com>
To: Peter Xu <peterx@redhat.com>
Cc: "Muhammad Usama Anjum" <usama.anjum@collabora.com>,
	"David Hildenbrand" <david@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Michał Mirosław" <emmir@google.com>,
	"Andrei Vagin" <avagin@gmail.com>,
	"Danylo Mocherniuk" <mdanylo@google.com>,
	"Paul Gofman" <pgofman@codeweavers.com>,
	"Cyrill Gorcunov" <gorcunov@gmail.com>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Shuah Khan" <shuah@kernel.org>,
	"Christian Brauner" <brauner@kernel.org>,
	"Yang Shi" <shy828301@gmail.com>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Liam R . Howlett" <Liam.Howlett@oracle.com>,
	"Yun Zhou" <yun.zhou@windriver.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Alex Sierra" <alex.sierra@amd.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Pasha Tatashin" <pasha.tatashin@soleen.com>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Nadav Amit" <namit@vmware.com>,
	"Axel Rasmussen" <axelrasmussen@google.com>,
	"Gustavo A . R . Silva" <gustavoars@kernel.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
	"Greg KH" <gregkh@linuxfoundation.org>,
	kernel@collabora.com
Subject: Re: [PATCH v7 3/4] fs/proc/task_mmu: Implement IOCTL to get and/or the clear info about PTEs
Date: Thu, 26 Jan 2023 19:32:53 +0500	[thread overview]
Message-ID: <e14875ff-7d59-ae24-9fb0-8169c54c7a17@collabora.com> (raw)
In-Reply-To: <Y9AVuF63y9UjEYcj@x1n>

On 1/24/23 10:30 PM, Peter Xu wrote:
> On Mon, Jan 23, 2023 at 05:18:13PM +0500, Muhammad Usama Anjum wrote:
>>>> +	if (IS_GET_OP(p) && p->max_pages && (p->found_pages == p->max_pages))
>>>> +		return -ENOSPC;
>>>
>>> This is the function to test "whether the walker should walk the vma
>>> specified".  This check should IIUC be meaningless because found_pages
>>> doesn't boost during vma switching, while OTOH your pmd walker fn should do
>>> proper check when increasing found_pages and return -ENOSPC properly when
>>> the same condition met.  That should be enough, IMHO.
>> This check is needed in case we want to abort the walk at once. We return
>> negative value from here which aborts the walk. Returning negative value
>> from pmd_entry doesn't abort the walk. So this check is needed in the
>> test_walk.
> 
> Why?  What I see locally is (walk_pmd_range):
> 
> 		if (ops->pmd_entry)
> 			err = ops->pmd_entry(pmd, addr, next, walk);
> 		if (err)
> 			break;
Sorry, mistake on my part. I'll correct it in next version (v9).

> 
> Thanks,
> 

-- 
BR,
Muhammad Usama Anjum