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Revert "riscv: mm: support Svnapot in huge vmap"

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This reverts commit ce173474cf.

We cannot correctly deal with NAPOT mappings in vmalloc/vmap because if
some part of a NAPOT mapping is unmapped, the remaining mapping is not
updated accordingly. For example:

ptr = vmalloc_huge(64 * 1024, GFP_KERNEL);
vunmap_range((unsigned long)(ptr + PAGE_SIZE),
	     (unsigned long)(ptr + 64 * 1024));

leads to the following kernel page table dump:

0xffff8f8000ef0000-0xffff8f8000ef1000    0x00000001033c0000         4K PTE N   ..     ..   D A G . . W R V

Meaning the first entry which was not unmapped still has the N bit set,
which, if accessed first and cached in the TLB, could allow access to the
unmapped range.

That's because the logic to break the NAPOT mapping does not exist and
likely won't. Indeed, to break a NAPOT mapping, we first have to clear
the whole mapping, flush the TLB and then set the new mapping ("break-
before-make" equivalent). That works fine in userspace since we can handle
any pagefault occurring on the remaining mapping but we can't handle a kernel
pagefault on such mapping.

So fix this by reverting the commit that introduced the vmap/vmalloc
support.

Fixes: ce173474cf ("riscv: mm: support Svnapot in huge vmap")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240227205016.121901-2-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Alexandre Ghiti 2024-02-27 21:50:15 +01:00 committed by Palmer Dabbelt
parent 6613476e22
commit 16ab4646c9
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GPG Key ID: 2E1319F35FBB1889
1 changed files with 1 additions and 60 deletions
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61
arch/riscv/include/asm/vmalloc.h
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@ -19,65 +19,6 @@ static inline bool arch_vmap_pmd_supported(pgprot_t prot)
return true;
}
#ifdef CONFIG_RISCV_ISA_SVNAPOT
#include <linux/pgtable.h>
#endif
#define arch_vmap_pte_range_map_size arch_vmap_pte_range_map_size
static inline unsigned long arch_vmap_pte_range_map_size(unsigned long addr, unsigned long end,
u64 pfn, unsigned int max_page_shift)
{
unsigned long map_size = PAGE_SIZE;
unsigned long size, order;
if (!has_svnapot())
return map_size;
for_each_napot_order_rev(order) {
if (napot_cont_shift(order) > max_page_shift)
continue;
size = napot_cont_size(order);
if (end - addr < size)
continue;
if (!IS_ALIGNED(addr, size))
continue;
if (!IS_ALIGNED(PFN_PHYS(pfn), size))
continue;
map_size = size;
break;
}
return map_size;
}
#define arch_vmap_pte_supported_shift arch_vmap_pte_supported_shift
static inline int arch_vmap_pte_supported_shift(unsigned long size)
{
int shift = PAGE_SHIFT;
unsigned long order;
if (!has_svnapot())
return shift;
WARN_ON_ONCE(size >= PMD_SIZE);
for_each_napot_order_rev(order) {
if (napot_cont_size(order) > size)
continue;
if (!IS_ALIGNED(size, napot_cont_size(order)))
continue;
shift = napot_cont_shift(order);
break;
}
return shift;
}
#endif /* CONFIG_RISCV_ISA_SVNAPOT */
#endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
#endif /* _ASM_RISCV_VMALLOC_H */