Conversation
ljs

Lorenzo Stoakes

Learning the hard way why pfn_valid() matters :)
1
0
2
hyeyoo

Hyeonggon Yoo

Reply to @ljs
Edited 1 year ago
@ljs when does it matter? the only thing I know about it is that the kernel does not have struct page when pfn_valid() is false.
2
0
1
ljs

Lorenzo Stoakes

Reply to @hyeyoo
@hyeyoo it matters when your pfn is garbage because your struct page* is uninitialised data :>)
0
0
2
hyeyoo

Hyeonggon Yoo

Reply to
@ptesarik @ljs

When do usable PFNs (for which pfn_valid() is false) exist?
2
0
1
ljs

Lorenzo Stoakes

Reply to @hyeyoo
@hyeyoo @ptesarik it's going to be arch-dependent. For x86-64 it always implies the PFN is garbage because it'd be > max physical range.

Am curious as to what particular scenario Petr is referring to though, I see some arches have a PFN offset which maybe leaves out usable PFNs?
1
0
1
ljs

Lorenzo Stoakes

Reply to
@ptesarik @hyeyoo ah yeah with MMIO I guess all bets are off :)
0
0
2
hyeyoo

Hyeonggon Yoo

Reply to @hyeyoo
Edited 1 year ago
@ptesarik @ljs

I thought maybe freeing unnecessary vmemmap pages for HugeTLB pages might be the case, but it seems to remap to first vmemmap page. And if I am not mistaken pfn_valid() will return true for them.
1
0
0
ljs

Lorenzo Stoakes

Reply to @hyeyoo
@hyeyoo @ptesarik that'd be ram-backed though right?
1
0
1
hyeyoo

Hyeonggon Yoo

Reply to @ljs
Edited 1 year ago
@ljs @ptesarik Yes! "might be the case" was was not clear ;)
0
0
1
About social.kernel.org

Terms of service

  1. Please do not use this service in violation of the Linux Kernel Code of Conduct. Doing so will result in your account suspension with the referral of the matter to the CoC committee.

  2. "Repeating"/"boosting" someone else's status on this platform will be treated as endorsement and will fall under rule #1.

  3. You are encouraged to use this platform to promote your work on the Linux Kernel, but there is no restriction on permitted topics (with the exception of anything covered by #1 above).

  4. There is no requirement to post in English, but it should be considered the primary language of communication on this platform.

Privacy notice

The admins of this service have access to all posted statuses. They aren't looking, but if it's something they shouldn't know about, then you should not post it on this platform.

Please see the Linux Foundation Privacy Policy, which applies to this platform as well.

Getting your own account

If you would like an account on this instance, please check that the following applies to you:

  • You are listed in MAINTAINERS or CREDITS

  • OR: You have a kernel.org account or email address

  • OR: You have a long and established history of involvement with the Linux Kernel

If the above is true and you agree with the Terms of Service and Privacy Notice listed above, please use these instructions to request an account: