Re: [PATCH v3 07/30] kho: add interfaces to unpreserve folios and physical memory ranges
From: Jason Gunthorpe <jgg@nvidia.com>
Date: 2025-08-14 13:22:37
Also in:
linux-doc, linux-fsdevel, linux-mm, lkml
On Thu, Aug 07, 2025 at 01:44:13AM +0000, Pasha Tatashin wrote:
+int kho_unpreserve_phys(phys_addr_t phys, size_t size)
+{
Why are we adding phys apis? Didn't we talk about this before and
agree not to expose these?
The places using it are goofy:
+static int luo_fdt_setup(void)
+{
+ fdt_out = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
+ get_order(LUO_FDT_SIZE));
+ ret = kho_preserve_phys(__pa(fdt_out), LUO_FDT_SIZE);
+ WARN_ON_ONCE(kho_unpreserve_phys(__pa(fdt_out), LUO_FDT_SIZE));
It literally allocated a page and then for some reason switches to
phys with an open coded __pa??
This is ugly, if you want a helper to match __get_free_pages() then
make one that works on void * directly. You can get the order of the
void * directly from the struct page IIRC when using GFP_COMP.
Which is perhaps another comment, if this __get_free_pages() is going
to be a common pattern (and I guess it will be) then the API should be
streamlined alot more:
void *kho_alloc_preserved_memory(gfp, size);
void kho_free_preserved_memory(void *);
Which can wrapper the get_free_pages and the preserve logic and gives
a nice path to possibly someday supporting non-PAGE_SIZE allocations.
Jason