Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/41957 ) Change subject: device: Introduce RESOURCE_ALLOCATION_TOP_DOWN ...................................................................... Patch Set 2: (1 comment) https://review.coreboot.org/c/coreboot/+/41957/2/src/lib/memrange.c File src/lib/memrange.c: https://review.coreboot.org/c/coreboot/+/41957/2/src/lib/memrange.c@430 PS2, Line 430: *stolen_base = ALIGN_DOWN(range_entry_end(r) - size, POWER_OF_2(align));
Don't we need to handle the from_top logic in memranges_find_entry() for region size checking? We're […] Then, let me convince you. :)
The check in memranges_find_entry() guarantees that there is enough (>= size) space between `r->begin` aligned up and `r->end`. Thus, `r->end + 1 - size` is above or equal to `r->begin` aligned up. And aligning it down would result in `r->begin` aligned up in the worst case. Long story: I guess what we have to prove is that every `stolen_base` with (1) stolen_base = ALIGN_DOWN(range_entry_end(r) - size, POWER_OF_2(align)) is above `r->begin` (2) stolen_base >= r->begin We divide (1) into two cases: (1.1) range_entry_end(r) - size < ALIGN_UP(r->begin, POWER_OF_2(align)) (1.2) range_entry_end(r) - size >= ALIGN_UP(r->begin, POWER_OF_2(align)) (1.1) is what we check in memranges_find_entry(). For (1.2) we can see via (1) (3) stolen_base >= ALIGN_DOWN(ALIGN_UP(r->begin, POWER_OF_2(align), POWER_OF_2(align)) Aligning down what is already aligned has no effect, thus (4) stolen_base >= ALIGN_UP(r->begin, POWER_OF_2(align)) >= r->begin -- To view, visit https://review.coreboot.org/c/coreboot/+/41957 To unsubscribe, or for help writing mail filters, visit https://review.coreboot.org/settings Gerrit-Project: coreboot Gerrit-Branch: master Gerrit-Change-Id: Iaf463d3e6b37d52e46761d8e210034fded58a8a4 Gerrit-Change-Number: 41957 Gerrit-PatchSet: 2 Gerrit-Owner: Nico Huber <nico.h@gmx.de> Gerrit-Reviewer: build bot (Jenkins) <no-reply@coreboot.org> Gerrit-CC: Aaron Durbin <adurbin@chromium.org> Gerrit-Comment-Date: Tue, 02 Jun 2020 11:56:49 +0000 Gerrit-HasComments: Yes Gerrit-Has-Labels: No Comment-In-Reply-To: Aaron Durbin <adurbin@chromium.org> Gerrit-MessageType: comment