[SYSDM] Prevent my german-teacher from getting a heart-attack by that misplaced comma.
[SMSS] Prevent myself from getting a heart-attack by that superfluous dot.
Furthermore this addendum serves the purpose of actually linking both PRs
and their 4 previous commits to the actual JIRA ticket CORE-18754, which wasn't
the case before:
0.4.15-dev-5392-g 04b2d35f5b
0.4.15-dev-5391-g a8e06d92e8
0.4.15-dev-5390-g a4274ad548
0.4.15-dev-5389-g 5dc43c0f32
What we have:
- Maximum number of pagefiles: 16
- Minimum pagefile size: 256 pages (1 MB when page size = 4096 bytes)
- Maximum pagefile size:
* 32-bit platforms: (1024 * 1024 - 1) pages (~ 4095 MB)
* x86 with PAE support: same size as for AMD x64
* x64 platform: (4 * 1024 * 1024 * 1024 - 1) pages (~ 16 TB)
* IA64 platform: (8 * 1024 * 1024 * 1024 - 1) pages (~ 32 TB)
Those are the values as supported and verified by the NT kernel.
Now, user-mode programs (including SMSS.EXE) have different opinions
on these, namely, they consider estimates directly in MB, respectively:
4095 MB, (16 * 1024 * 1024) MB, and (32 * 1024 * 1024) MB
(verified on Win2k3 and Win7 32 and 64 bits).
Also here, the minimum pagefile size is set to 2 MB.
Starting Windows 8+ (and 10), those values change slightly, and are
still not fully synchronized between NTOS:MM and SMSS. Finally, while
(x86 PAE and) AMD64 and ARM64 seem to share the maximum pagefile
size limit, 32-bit ARMv7 appears to use different limits than regular
x86 (2 GB instead of 4).
Please keep those values as they are for NT compatibility!
See the following references:
https://www.geoffchappell.com/studies/windows/km/ntoskrnl/api/mm/modwrite/create.htmhttps://techcommunity.microsoft.com/t5/ask-the-performance-team/what-is-the-page-file-for-anyway/ba-p/372608
+ Manual extraction of the values from different NT 6.2,6.3,10 builds.
[SMSS] Fill out in particular the x86-specific case for PAE.
[NTOS:MM] Some cleanup in the NtCreatePagingFile() code, namely:
- Clarify some comments;
- Validate the lower and upper bounds of the Minimum and Maximum sizes
(based on Windows behaviour as explained by Geoff + manual tests).
- Open the pagefile in case-insensitive;
- Simplify the loop that finds an existing matching pagefile;
- Simplify some failure exit paths;
- Add a "Missing validation steps TODO" comment block explaining the
existing code-hole.
64 MB used to be enough to at least finish 2nd stage, but that does not
always seem to be the case anymore. Leaving this little free space does
not make for a good user experience either way.
256 MB is still not much, but at least provides slightly more usability.
The PROCESS_DEVICEMAP_INFORMATION union has 2 fields, one is a handle, the other one is a structure of 36 bytes (independent of architecture). The handle forces 64 bit alignment on 64 bit builds, making the structure 4 bytes bigger than on 32 bit builds. The site is checked in NtQueryInformationProcess (case ProcessDeviceMap). The expected size on x64 is the size of the Query structure without alignment. autocheck correctly passes the site of the Query union member, while smss passes the full size of PROCESS_DEVICEMAP_INFORMATION. Packing the structure is not an option, since it is defined in public headers without packing. Using the original headers sizeof(PROCESS_DEVICEMAP_INFORMATION) is 0x28, sizeof(PROCESS_DEVICEMAP_INFORMATION::Query) is 0x24.
