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powerpc/mm: Move the DSISR_PROTFAULT sanity check 

This has a page of comment explaining what's going on right in
the middle of do_page_fault() which makes things a bit hard to
follow. Move it to a helper instead. Also do the test earlier
as there's no point waiting until after we found the VMA.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Benjamin Herrenschmidt 2017-07-19 14:49:39 +10:00 committed by Michael Ellerman
parent 04aafdc601
commit 2865d08dd9
1 changed files with 42 additions and 33 deletions
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75
arch/powerpc/mm/fault.c
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@ -239,6 +239,45 @@ static inline void cmo_account_page_fault(void)
static inline void cmo_account_page_fault(void) { } static inline void cmo_account_page_fault(void) { }
#endif /* CONFIG_PPC_SMLPAR */ #endif /* CONFIG_PPC_SMLPAR */
#ifdef CONFIG_PPC_STD_MMU
static void sanity_check_fault(bool is_write, unsigned long error_code)
{
/*
* For hash translation mode, we should never get a
* PROTFAULT. Any update to pte to reduce access will result in us
* removing the hash page table entry, thus resulting in a DSISR_NOHPTE
* fault instead of DSISR_PROTFAULT.
*
* A pte update to relax the access will not result in a hash page table
* entry invalidate and hence can result in DSISR_PROTFAULT.
* ptep_set_access_flags() doesn't do a hpte flush. This is why we have
* the special !is_write in the below conditional.
*
* For platforms that doesn't supports coherent icache and do support
* per page noexec bit, we do setup things such that we do the
* sync between D/I cache via fault. But that is handled via low level
* hash fault code (hash_page_do_lazy_icache()) and we should not reach
* here in such case.
*
* For wrong access that can result in PROTFAULT, the above vma->vm_flags
* check should handle those and hence we should fall to the bad_area
* handling correctly.
*
* For embedded with per page exec support that doesn't support coherent
* icache we do get PROTFAULT and we handle that D/I cache sync in
* set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
* is conditional for server MMU.
*
* For radix, we can get prot fault for autonuma case, because radix
* page table will have them marked noaccess for user.
*/
if (!radix_enabled() && !is_write)
WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
}
#else
static void sanity_check_fault(bool is_write, unsigned long error_code) { }
#endif /* CONFIG_PPC_STD_MMU */
/* /*
* Define the correct "is_write" bit in error_code based * Define the correct "is_write" bit in error_code based
* on the processor family * on the processor family
@ -306,6 +345,9 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
return SIGBUS; return SIGBUS;
} }
/* Additional sanity check(s) */
sanity_check_fault(is_write, error_code);
/* /*
* The kernel should never take an execute fault nor should it * The kernel should never take an execute fault nor should it
* take a page fault to a kernel address. * take a page fault to a kernel address.
@ -441,39 +483,6 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))) if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
return bad_area(regs, address); return bad_area(regs, address);
} }
#ifdef CONFIG_PPC_STD_MMU
/*
* For hash translation mode, we should never get a
* PROTFAULT. Any update to pte to reduce access will result in us
* removing the hash page table entry, thus resulting in a DSISR_NOHPTE
* fault instead of DSISR_PROTFAULT.
*
* A pte update to relax the access will not result in a hash page table
* entry invalidate and hence can result in DSISR_PROTFAULT.
* ptep_set_access_flags() doesn't do a hpte flush. This is why we have
* the special !is_write in the below conditional.
*
* For platforms that doesn't supports coherent icache and do support
* per page noexec bit, we do setup things such that we do the
* sync between D/I cache via fault. But that is handled via low level
* hash fault code (hash_page_do_lazy_icache()) and we should not reach
* here in such case.
*
* For wrong access that can result in PROTFAULT, the above vma->vm_flags
* check should handle those and hence we should fall to the bad_area
* handling correctly.
*
* For embedded with per page exec support that doesn't support coherent
* icache we do get PROTFAULT and we handle that D/I cache sync in
* set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
* is conditional for server MMU.
*
* For radix, we can get prot fault for autonuma case, because radix
* page table will have them marked noaccess for user.
*/
if (!radix_enabled() && !is_write)
WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
#endif /* CONFIG_PPC_STD_MMU */
/* /*
* If for any reason at all we couldn't handle the fault, * If for any reason at all we couldn't handle the fault,