On Fri, Apr 25, 2025 at 09:48:50PM +0200, David Hildenbrand wrote: > On 25.04.25 21:31, Peter Xu wrote: > > On Fri, Apr 25, 2025 at 10:17:06AM +0200, David Hildenbrand wrote: > > > ... by factoring it out from track_pfn_remap(). > > > > > > For PMDs/PUDs, actually check the full range, and trigger a fallback > > > if we run into this "different memory types / cachemodes" scenario. > > > > The current patch looks like to still pass PAGE_SIZE into the new helper at > > all track_pfn_insert() call sites, so it seems this comment does not 100% > > match with the code? Or I may have misread somewhere. > > No, you're right, while reshuffling the patches I forgot to add the actual > PMD/PUD size. > > > > > Maybe it's still easier to keep the single-pfn lookup to never fail.. more > > below. > > > > [...] > > > > /* > > > @@ -1556,8 +1553,23 @@ static inline void untrack_pfn_clear(struct > > > vm_area_struct *vma) > > > extern int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot, > > > unsigned long pfn, unsigned long addr, > > > unsigned long size); > > > -extern void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot, > > > - pfn_t pfn); > > > + > > > +/** > > > + * pfnmap_sanitize_pgprot - sanitize the pgprot for a pfn range > > > > Nit: s/sanitize/update|setup|.../? > > > > But maybe you have good reason to use sanitize. No strong opinions. > > What it does on PAT (only implementation so far ...) is looking up the > memory type to select the caching mode that can be use. > > "sanitize" was IMHO a good fit, because we must make sure that we don't use > the wrong caching mode. > > update/setup/... don't make that quite clear. Any other suggestions?
I'm very poor on naming.. :( So far anything seems slightly better than sanitize to me, as the word "sanitize" is actually also used in memtype.c for other purpose.. see sanitize_phys(). > > > > > > + * @pfn: the start of the pfn range > > > + * @size: the size of the pfn range > > > + * @prot: the pgprot to sanitize > > > + * > > > + * Sanitize the given pgprot for a pfn range, for example, adjusting the > > > + * cachemode. > > > + * > > > + * This function cannot fail for a single page, but can fail for multiple > > > + * pages. > > > + * > > > + * Returns 0 on success and -EINVAL on error. > > > + */ > > > +int pfnmap_sanitize_pgprot(unsigned long pfn, unsigned long size, > > > + pgprot_t *prot); > > > extern int track_pfn_copy(struct vm_area_struct *dst_vma, > > > struct vm_area_struct *src_vma, unsigned long *pfn); > > > extern void untrack_pfn_copy(struct vm_area_struct *dst_vma, > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > index fdcf0a6049b9f..b8ae5e1493315 100644 > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > @@ -1455,7 +1455,9 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, > > > pfn_t pfn, bool write) > > > return VM_FAULT_OOM; > > > } > > > - track_pfn_insert(vma, &pgprot, pfn); > > > + if (pfnmap_sanitize_pgprot(pfn_t_to_pfn(pfn), PAGE_SIZE, &pgprot)) > > > + return VM_FAULT_FALLBACK; > > > > Would "pgtable" leak if it fails? If it's PAGE_SIZE, IIUC it won't ever > > trigger, though. > > > > Maybe we could have a "void pfnmap_sanitize_pgprot_pfn(&pgprot, pfn)" to > > replace track_pfn_insert() and never fail? Dropping vma ref is definitely > > a win already in all cases. > > It could be a simple wrapper around pfnmap_sanitize_pgprot(), yes. That's > certainly helpful for the single-page case. > > Regarding never failing here: we should check the whole range. We have to > make sure that none of the pages has a memory type / caching mode that is > incompatible with what we setup. Would it happen in real world? IIUC per-vma registration needs to happen first, which checks for memtype conflicts in the first place, or reserve_pfn_range() could already have failed. Here it's the fault path looking up the memtype, so I would expect it is guaranteed all pfns under the same vma is following the verified (and same) memtype? Thanks, -- Peter Xu
