mm/access_process_vm: use the new follow_pfnmap API

JIRA: https://issues.redhat.com/browse/RHEL-73613

commit b17269a
Author: Peter Xu <peterx@redhat.com>
Date:   Mon Aug 26 16:43:49 2024 -0400

    mm/access_process_vm: use the new follow_pfnmap API

    Use the new API that can understand huge pfn mappings.

    Link: https://lkml.kernel.org/r/20240826204353.2228736-16-peterx@redhat.com
    Signed-off-by: Peter Xu <peterx@redhat.com>
    Cc: Alexander Gordeev <agordeev@linux.ibm.com>
    Cc: Alex Williamson <alex.williamson@redhat.com>
    Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: David Hildenbrand <david@redhat.com>
    Cc: Gavin Shan <gshan@redhat.com>
    Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
    Cc: Heiko Carstens <hca@linux.ibm.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Jason Gunthorpe <jgg@nvidia.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Niklas Schnelle <schnelle@linux.ibm.com>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Ryan Roberts <ryan.roberts@arm.com>
    Cc: Sean Christopherson <seanjc@google.com>
    Cc: Sven Schnelle <svens@linux.ibm.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vasily Gorbik <gor@linux.ibm.com>
    Cc: Will Deacon <will@kernel.org>
    Cc: Zi Yan <ziy@nvidia.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Donald Dutile <ddutile@redhat.com>

Author: ddutile

mm/memory.c

@@ -5839,34 +5839,34 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
 	resource_size_t phys_addr;
 	unsigned long prot = 0;
 	void __iomem *maddr;
-	pte_t *ptep, pte;
-	spinlock_t *ptl;
 	int offset = offset_in_page(addr);
 	int ret = -EINVAL;
+	bool writable;
+	struct follow_pfnmap_args args = { .vma = vma, .address = addr };
 
 retry:
-	if (follow_pte(vma, addr, &ptep, &ptl))
+	if (follow_pfnmap_start(&args))
 		return -EINVAL;
-	pte = ptep_get(ptep);
-	pte_unmap_unlock(ptep, ptl);
+	prot = pgprot_val(args.pgprot);
+	phys_addr = (resource_size_t)args.pfn << PAGE_SHIFT;
+	writable = args.writable;
+	follow_pfnmap_end(&args);
 
-	prot = pgprot_val(pte_pgprot(pte));
-	phys_addr = (resource_size_t)pte_pfn(pte) << PAGE_SHIFT;
-
-	if ((write & FOLL_WRITE) && !pte_write(pte))
+	if ((write & FOLL_WRITE) && !writable)
 		return -EINVAL;
 
 	maddr = ioremap_prot(phys_addr, PAGE_ALIGN(len + offset), prot);
 	if (!maddr)
 		return -ENOMEM;
 
-	if (follow_pte(vma, addr, &ptep, &ptl))
+	if (follow_pfnmap_start(&args))
 		goto out_unmap;
 
-	if (!pte_same(pte, ptep_get(ptep))) {
-		pte_unmap_unlock(ptep, ptl);
+	if ((prot != pgprot_val(args.pgprot)) ||
+	    (phys_addr != (args.pfn << PAGE_SHIFT)) ||
+	    (writable != args.writable)) {
+		follow_pfnmap_end(&args);
 		iounmap(maddr);
-
 		goto retry;
 	}
 
@@ -5875,7 +5875,7 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
 	else
 		memcpy_fromio(buf, maddr + offset, len);
 	ret = len;
-	pte_unmap_unlock(ptep, ptl);
+	follow_pfnmap_end(&args);
 out_unmap:
 	iounmap(maddr);