Revert "x86/mm: Introduce lookup_address_in_mm()"

Drop lookup_address_in_mm() now that KVM is providing it's own variant
of lookup_address_in_pgd() that is safe for use with user addresses, e.g.
guards against page tables being torn down. A variant that provides a
non-init mm is inherently dangerous and flawed, as the only reason to use
an mm other than init_mm is to walk a userspace mapping, and
lookup_address_in_pgd() does not play nice with userspace mappings, e.g.
doesn't disable IRQs to block TLB shootdowns and doesn't use READ_ONCE()
to ensure an upper level entry isn't converted to a huge page between
checking the PAGE_SIZE bit and grabbing the address of the next level
down.

This reverts commit 13c72c060f1ba6f4eddd7b1c4f52a8aded43d6d9.

Signed-off-by: Sean Christopherson <[e-mail]>
Message-Id: <YmwIi3bXr/1yhYV/@google.com>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/include/asm/pgtable_types.h

···
 extern pte_t *lookup_address(unsigned long address, unsigned int *level);
 extern pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
 				    unsigned int *level);
-
-struct mm_struct;
-extern pte_t *lookup_address_in_mm(struct mm_struct *mm, unsigned long address,
-				   unsigned int *level);
 extern pmd_t *lookup_pmd_address(unsigned long address);
 extern phys_addr_t slow_virt_to_phys(void *__address);
 extern int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn,

arch/x86/mm/pat/set_memory.c

···
 }
 EXPORT_SYMBOL_GPL(lookup_address);
 
-/*
- * Lookup the page table entry for a virtual address in a given mm. Return a
- * pointer to the entry and the level of the mapping.
- */
-pte_t *lookup_address_in_mm(struct mm_struct *mm, unsigned long address,
-			    unsigned int *level)
-{
-	return lookup_address_in_pgd(pgd_offset(mm, address), address, level);
-}
-EXPORT_SYMBOL_GPL(lookup_address_in_mm);
-
 static pte_t *_lookup_address_cpa(struct cpa_data *cpa, unsigned long address,
 				  unsigned int *level)
 {