s390: enable HAVE_IOREMAP_PROT

In commit b02002cc4c0f ("s390/pci: Implement ioremap_wc/prot() with
MIO") we implemented both ioremap_wc() and ioremap_prot() however until
now we had not set HAVE_IOREMAP_PROT in Kconfig, do so now.

This also requires implementing pte_pgprot() as this is used in the
generic_access_phys() code enabled by CONFIG_HAVE_IOREMAP_PROT. As with
ioremap_wc() we need to take the MMIO Write Back bit index into account.

Moreover since the pgprot value returned from pte_pgprot() is to be used
for mappings into kernel address space we must make sure that it uses
appropriate kernel page table protection bits. In particular a pgprot
value originally coming from userspace could have the _PAGE_PROTECT
bit set to enable fault based dirty bit accounting which would then make
the mapping inaccessible when used in kernel address space.

Fixes: b02002cc4c0f ("s390/pci: Implement ioremap_wc/prot() with MIO")
Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 29c7ecd5ad1d..9512f6820ead 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -866,6 +866,25 @@ static inline int pte_unused(pte_t pte)
 }
 
 /*
+ * Extract the pgprot value from the given pte while at the same time making it
+ * usable for kernel address space mappings where fault driven dirty and
+ * young/old accounting is not supported, i.e _PAGE_PROTECT and _PAGE_INVALID
+ * must not be set.
+ */
+static inline pgprot_t pte_pgprot(pte_t pte)
+{
+	unsigned long pte_flags = pte_val(pte) & _PAGE_CHG_MASK;
+
+	if (pte_write(pte))
+		pte_flags |= pgprot_val(PAGE_KERNEL);
+	else
+		pte_flags |= pgprot_val(PAGE_KERNEL_RO);
+	pte_flags |= pte_val(pte) & mio_wb_bit_mask;
+
+	return __pgprot(pte_flags);
+}
+
+/*
  * pgd/pmd/pte modification functions
  */