[PATCH v3 3/5] x86/mm: add help function to check specific protection flags in range

Bin Yang
2018-08-21T01:16:46Z

Introduce the needs_static_protections() helper to check specific
protection flags in range. It calls static_protection() to check
whether any part of the address/len range is forced to change from 'prot'.

Suggested-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Bin Yang <bin.yang@intel.com>
---
arch/x86/mm/pageattr.c | 36 +++++++++++++++++++++++++++---------
1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 091f1d3..f630eb4 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -367,6 +367,30 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
}

/*
+ * static_protections() "forces" page protections for some address
+ * ranges. Return true if any part of the address/len range is forced
+ * to change from 'prot'.
+ */
+static inline bool
+needs_static_protections(pgprot_t prot, unsigned long address,
+ unsigned long len, unsigned long pfn)
+{
+ int i;
+
+ address &= PAGE_MASK;
+ len = PFN_ALIGN(len);
+ for (i = 0; i < (len >> PAGE_SHIFT); i++, address += PAGE_SIZE, pfn++) {
+ pgprot_t chk_prot = static_protections(prot, address, pfn);
+
+ if (pgprot_val(chk_prot) != pgprot_val(prot))
+ return true;
+ }
+
+ /* Does static_protections() demand a change ? */
+ return false;
+}
+
+/*
* Lookup the page table entry for a virtual address in a specific pgd.
* Return a pointer to the entry and the level of the mapping.
*/
@@ -556,7 +580,7 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
unsigned long nextpage_addr, numpages, pmask, psize, addr, pfn, old_pfn;
pte_t new_pte, old_pte, *tmp;
pgprot_t old_prot, new_prot, req_prot;
- int i, do_split = 1;
+ int do_split = 1;
enum pg_level level;

if (cpa->force_split)
@@ -660,14 +684,8 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
* static_protection() requires a different pgprot for one of
* the pages in the range we try to preserve:
*/
- pfn = old_pfn;
- for (i = 0; i < (psize >> PAGE_SHIFT); i++, addr += PAGE_SIZE, pfn++) {
- pgprot_t chk_prot = static_protections(req_prot, addr, pfn);
-
- if (pgprot_val(chk_prot) != pgprot_val(new_prot))
- goto out_unlock;
- }
-
+ if (needs_static_protections(new_prot, addr, psize, old_pfn))
+ goto out_unlock;

/* All checks passed. Just change the large mapping entry */
new_pte = pfn_pte(old_pfn, new_prot);
--
2.7.4