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ANDROID: 16K: Don't set padding vm_flags on 32-bit archs

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vma_pad_fixup_flags() and is_mergable_pad_vma() were inadvertently
affecting the vm_flags on 32-bit arch, making some VMAs not mergable.

This causes zygote to crash as the Art GC's heap compaction fails.

The compaction depends on mremap() which will fail when operating on
a range that spans multiple VMAs [1]. This can happen now due to the
incorrect is_mergable_pad_vma() check.

Make all the pgsize_migration APIs no-ops in 32-bit architectures,
since Android only performs ELF segment extension in 64-bit archs.

[1] https://github.com/torvalds/linux/blob/v6.9/mm/mremap.c#L841-L843

Bug: 353667356
Change-Id: Id9b0076ef173d75a4afc85577355d340fce03e65
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
(cherry picked from commit f3437db87063f624f189e1cd38347a971fdd3fa0)
This commit is contained in:
Kalesh Singh 2024-07-17 23:06:48 +00:00
parent dc1385281a
commit adc9210e7e
2 changed files with 48 additions and 22 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

38
include/linux/pgsize_migration.h
View file

@ -62,6 +62,14 @@ extern void show_map_pad_vma(struct vm_area_struct *vma,
extern void split_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *new,
unsigned long addr, int new_below);
extern unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
unsigned long newflags);
extern bool is_mergable_pad_vma(struct vm_area_struct *vma,
unsigned long vm_flags);
extern unsigned long vma_data_pages(struct vm_area_struct *vma);
#else /* PAGE_SIZE != SZ_4K || !defined(CONFIG_64BIT) */
static inline void vma_set_pad_pages(struct vm_area_struct *vma,
unsigned long nr_pages)
@ -98,36 +106,22 @@ static inline void split_pad_vma(struct vm_area_struct *vma, struct vm_area_stru
unsigned long addr, int new_below)
{
}
#endif /* PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT) */
static inline unsigned long vma_data_pages(struct vm_area_struct *vma)
{
return vma_pages(vma) - vma_pad_pages(vma);
}
/*
* Sets the correct padding bits / flags for a VMA split.
*/
static inline unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
unsigned long newflags)
{
if (newflags & VM_PAD_MASK)
return (newflags & ~VM_PAD_MASK) | (vma->vm_flags & VM_PAD_MASK);
else
return newflags;
return newflags;
}
/*
* Merging of padding VMAs is uncommon, as padding is only allowed
* from the linker context.
*
* To simplify the semantics, adjacent VMAs with padding are not
* allowed to merge.
*/
static inline bool is_mergable_pad_vma(struct vm_area_struct *vma,
unsigned long vm_flags)
{
/* Padding VMAs cannot be merged with other padding or real VMAs */
return !((vma->vm_flags | vm_flags) & VM_PAD_MASK);
return true;
}
static inline unsigned long vma_data_pages(struct vm_area_struct *vma)
{
return vma_pages(vma);
}
#endif /* PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT) */
#endif /* _LINUX_PAGE_SIZE_MIGRATION_H */

32
mm/pgsize_migration.c
View file

@ -405,5 +405,37 @@ void split_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *new,
vma_set_pad_pages(second, nr_vma2_pages);
}
}
/*
* Sets the correct padding bits / flags for a VMA split.
*/
unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
unsigned long newflags)
{
if (newflags & VM_PAD_MASK)
return (newflags & ~VM_PAD_MASK) | (vma->vm_flags & VM_PAD_MASK);
else
return newflags;
}
/*
* Merging of padding VMAs is uncommon, as padding is only allowed
* from the linker context.
*
* To simplify the semantics, adjacent VMAs with padding are not
* allowed to merge.
*/
bool is_mergable_pad_vma(struct vm_area_struct *vma,
unsigned long vm_flags)
{
/* Padding VMAs cannot be merged with other padding or real VMAs */
return !((vma->vm_flags | vm_flags) & VM_PAD_MASK);
}
unsigned long vma_data_pages(struct vm_area_struct *vma)
{
return vma_pages(vma) - vma_pad_pages(vma);
}
#endif /* PAGE_SIZE == SZ_4K */
#endif /* CONFIG_64BIT */