x86/xen: do not use _PAGE_IOMAP PTE flag for I/O mappings

Since mfn_to_pfn() returns the correct PFN for identity mappings (as
used for MMIO regions), the use of _PAGE_IOMAP is not required in
pte_mfn_to_pfn().

Do not set the _PAGE_IOMAP flag in pte_pfn_to_mfn() and do not use it
in pte_mfn_to_pfn().

This will allow _PAGE_IOMAP to be removed, making it available for
future use.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/mmu.c

@@ -399,38 +399,14 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
 		if (unlikely(mfn == INVALID_P2M_ENTRY)) {
 			mfn = 0;
 			flags = 0;
-		} else {
-			/*
-			 * Paramount to do this test _after_ the
-			 * INVALID_P2M_ENTRY as INVALID_P2M_ENTRY &
-			 * IDENTITY_FRAME_BIT resolves to true.
-			 */
-			mfn &= ~FOREIGN_FRAME_BIT;
-			if (mfn & IDENTITY_FRAME_BIT) {
-				mfn &= ~IDENTITY_FRAME_BIT;
-				flags |= _PAGE_IOMAP;
-			}
-		}
+		} else
+			mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT);
 		val = ((pteval_t)mfn << PAGE_SHIFT) | flags;
 	}
 
 	return val;
 }
 
-static pteval_t iomap_pte(pteval_t val)
-{
-	if (val & _PAGE_PRESENT) {
-		unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
-		pteval_t flags = val & PTE_FLAGS_MASK;
-
-		/* We assume the pte frame number is a MFN, so
-		   just use it as-is. */
-		val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
-	}
-
-	return val;
-}
-
 __visible pteval_t xen_pte_val(pte_t pte)
 {
 	pteval_t pteval = pte.pte;
@@ -441,9 +417,6 @@ __visible pteval_t xen_pte_val(pte_t pte)
 		pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;
 	}
 #endif
-	if (xen_initial_domain() && (pteval & _PAGE_IOMAP))
-		return pteval;
-
 	return pte_mfn_to_pfn(pteval);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);
@@ -481,7 +454,6 @@ void xen_set_pat(u64 pat)
 
 __visible pte_t xen_make_pte(pteval_t pte)
 {
-	phys_addr_t addr = (pte & PTE_PFN_MASK);
 #if 0
 	/* If Linux is trying to set a WC pte, then map to the Xen WC.
 	 * If _PAGE_PAT is set, then it probably means it is really
@@ -496,19 +468,7 @@ __visible pte_t xen_make_pte(pteval_t pte)
 			pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT;
 	}
 #endif
-	/*
-	 * Unprivileged domains are allowed to do IOMAPpings for
-	 * PCI passthrough, but not map ISA space.  The ISA
-	 * mappings are just dummy local mappings to keep other
-	 * parts of the kernel happy.
-	 */
-	if (unlikely(pte & _PAGE_IOMAP) &&
-	    (xen_initial_domain() || addr >= ISA_END_ADDRESS)) {
-		pte = iomap_pte(pte);
-	} else {
-		pte &= ~_PAGE_IOMAP;
-		pte = pte_pfn_to_mfn(pte);
-	}
+	pte = pte_pfn_to_mfn(pte);
 
 	return native_make_pte(pte);
 }
@@ -2091,7 +2051,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
 
 	default:
 		/* By default, set_fixmap is used for hardware mappings */
-		pte = mfn_pte(phys, __pgprot(pgprot_val(prot) | _PAGE_IOMAP));
+		pte = mfn_pte(phys, prot);
 		break;
 	}