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s390/mm: Remove folio handling for kernel faults in do_secure_storage_access()

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Remove folio handling for secure storage access exceptions that happen
via the kernel mapping. Using folio_try_get() for exceptions via the
kernel mapping is racy: for example such an exception may happen on one
CPU, while a different CPU frees the corresponding page. Subsequently the
page can be part of a folio of different size, before the faulting CPU
executes folio_try_get(). This may lead to data corruption.

As of now this scenario does not seem to be possible, however with the
upcoming load_unaligned_zeropad() this is possible.

As a side effect PG_arch_1 is not cleared anymore for such faults via the
kernel mapping. However given that this bit is over-indicating it
shouldn't matter.

Tested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Heiko Carstens
2026-07-20 10:58:31 +02:00
committed by Vasily Gorbik
parent a2e5a9d853
commit ecb00aa6fb
1 changed files with 1 additions and 7 deletions
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8
arch/s390/mm/fault.c
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@@ -440,13 +440,7 @@ void do_secure_storage_access(struct pt_regs *regs)
if (is_kernel_fault(regs)) {
if (is_vmalloc_addr((void *)addr))
return handle_fault_error_nolock(regs, 0);
folio = virt_to_folio((void *)addr);
if (unlikely(!folio_try_get(folio)))
return;
rc = uv_convert_from_secure(folio_to_phys(folio));
if (!rc)
clear_bit(PG_arch_1, &folio->flags.f);
folio_put(folio);
rc = uv_convert_from_secure(__pa(addr));
/*
* There are some valid fixup types for kernel
* accesses to donated secure memory. zeropad is one