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R . Silva" , "Liam R . Howlett" , Matthew Wilcox , Mike Rapoport , Nadav Amit , Pasha Tatashin , Paul Gofman , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , Yang Shi , Yun Zhou , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, kernel@collabora.com Subject: Re: [v2] fs/proc/task_mmu: Implement IOCTL for efficient page table scanning Content-Language: en-US To: =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= References: <20230713101415.108875-6-usama.anjum@collabora.com> <7eedf953-7cf6-c342-8fa8-b7626d69ab63@collabora.com> <382f4435-2088-08ce-20e9-bc1a15050861@collabora.com> <44eddc7d-fd68-1595-7e4f-e196abe37311@collabora.com> From: Muhammad Usama Anjum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D40724000F X-Stat-Signature: 1o39orwikrho6b7xi765wtwnq4dk5qcd X-Rspam-User: X-HE-Tag: 1690276187-912527 X-HE-Meta: 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 mP9nvNjK aSQFeShSbIL+V1zxYa3p/+F691olZTox5W1IuY+ZmbQ9DwWnRoZ8eEEfOm/Td5IDUy9/+Xz037WjzcXgc/scUWVWfrdesa5DjjY6Ten9zxDQ9g2MYobu52qRZipIhATdHHMVIJW8IsrTHIA7Nll+m8/C7Qo8A1Zr3bO4htK6iV18TbQ9bGTXJVU0O7WukMP1ubQSY0aT4GEmm8TKCvATrlFGv/48VlW43CryPWZwz+qB7q75edsCWmsleOP7jx78T2dSu X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 7/25/23 12:23 PM, Muhammad Usama Anjum wrote: > On 7/24/23 9:10 PM, Michał Mirosław wrote: > [...]>>>> @@ -2219,22 +2225,24 @@ static int pagemap_scan_get_args(struct > pm_scan_arg >>>>> *arg, >>>>> arg->category_anyof_mask | arg->return_mask) & ~PM_SCAN_CATEGORIES) >>>>> return -EINVAL; >>>>> >>>>> - start = untagged_addr((unsigned long)arg->start); >>>>> - end = untagged_addr((unsigned long)arg->end); >>>>> - vec = untagged_addr((unsigned long)arg->vec); >>>>> + arg->start = untagged_addr((unsigned long)arg->start); >>>>> + arg->end = untagged_addr((unsigned long)arg->end); >>>>> + arg->vec = untagged_addr((unsigned long)arg->vec); >>>> >>>> BTW, We should we keep the tag in args writeback(). >>> Sorry what? >>> After this function, the start, end and vec would be used. We need to make >>> sure that the address are untagged before that. >> >> We do write back the address the walk ended at to arg->start in >> userspace. This pointer I think needs the tag reconstructed so that >> retrying the ioctl() will be possible. > Even if we reconstruct the tag for end and vec, We need to update the start > address. Can we just put same tag as original start in it? I'm not sure. The special users would use tags. If they are using it, they'll just re-add the tag in next invocation. I think this implementation is correct. > -- BR, Muhammad Usama Anjum