KVM: PPC: Use __kvm_faultin_pfn() to handle page faults on Book3s Radix

Replace Book3s Radix's homebrewed (read: copy+pasted) fault-in logic with
__kvm_faultin_pfn(), which functionally does pretty much the exact same
thing.

Note, when the code was written, KVM indeed didn't do fast GUP without
"!atomic && !async", but that has long since changed (KVM tries fast GUP
for all writable mappings).

Signed-off-by: Sean Christopherson <[e-mail]>
Tested-by: Dmitry Osipenko <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
Message-ID: <[e-mail]>

arch/powerpc/kvm/book3s_64_mmu_radix.c

···
 	unsigned long mmu_seq;
 	unsigned long hva, gfn = gpa >> PAGE_SHIFT;
 	bool upgrade_write = false;
-	bool *upgrade_p = &upgrade_write;
 	pte_t pte, *ptep;
 	unsigned int shift, level;
 	int ret;
 	bool large_enable;
+	kvm_pfn_t pfn;
 
 	/* used to check for invalidations in progress */
 	mmu_seq = kvm->mmu_invalidate_seq;
 	smp_rmb();
 
-	/*
-	 * Do a fast check first, since __gfn_to_pfn_memslot doesn't
-	 * do it with !atomic && !async, which is how we call it.
-	 * We always ask for write permission since the common case
-	 * is that the page is writable.
-	 */
 	hva = gfn_to_hva_memslot(memslot, gfn);
-	if (!kvm_ro && get_user_page_fast_only(hva, FOLL_WRITE, &page)) {
-		upgrade_write = true;
-	} else {
-		unsigned long pfn;
-
-		/* Call KVM generic code to do the slow-path check */
-		pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
-					   writing, upgrade_p);
-		if (is_error_noslot_pfn(pfn))
-			return -EFAULT;
-		page = NULL;
-		if (pfn_valid(pfn)) {
-			page = pfn_to_page(pfn);
-			if (PageReserved(page))
-				page = NULL;
-		}
-	}
+	pfn = __kvm_faultin_pfn(memslot, gfn, writing ? FOLL_WRITE : 0,
+				&upgrade_write, &page);
+	if (is_error_noslot_pfn(pfn))
+		return -EFAULT;
 
 	/*
 	 * Read the PTE from the process' radix tree and use that