[patch V2 01/10] x86/mm/cpa: Split, rename and clean up try_preserve_large_page()

Thomas Gleixner
2018-09-14T13:21:08Z

[-- Attachment #1: x86-mm-cpa--Split-try_preserve_large_page--.patch --]
[-- Type: text/plain, Size: 7653 bytes --]

Avoid the extra variable and gotos by splitting the function into the
actual algorithm and a callable function which contains the lock
protection.

Rename it to should_split_large_page() while at it so the return values make
actually sense.

Clean up the code flow, comments and general whitespace damage while at it. No
functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/mm/pageattr.c | 121 ++++++++++++++++++++++++-------------------------
1 file changed, 60 insertions(+), 61 deletions(-)

--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -421,18 +421,18 @@ pte_t *lookup_address_in_pgd(pgd_t *pgd,
*/
pte_t *lookup_address(unsigned long address, unsigned int *level)
{
- return lookup_address_in_pgd(pgd_offset_k(address), address, level);
+ return lookup_address_in_pgd(pgd_offset_k(address), address, level);
}
EXPORT_SYMBOL_GPL(lookup_address);

static pte_t *_lookup_address_cpa(struct cpa_data *cpa, unsigned long address,
unsigned int *level)
{
- if (cpa->pgd)
+ if (cpa->pgd)
return lookup_address_in_pgd(cpa->pgd + pgd_index(address),
address, level);

- return lookup_address(address, level);
+ return lookup_address(address, level);
}

/*
@@ -549,27 +549,22 @@ static pgprot_t pgprot_clear_protnone_bi
return prot;
}

-static int
-try_preserve_large_page(pte_t *kpte, unsigned long address,
- struct cpa_data *cpa)
+static int __should_split_large_page(pte_t *kpte, unsigned long address,
+ struct cpa_data *cpa)
{
- unsigned long nextpage_addr, numpages, pmask, psize, addr, pfn, old_pfn;
- pte_t new_pte, old_pte, *tmp;
+ unsigned long numpages, pmask, psize, lpaddr, addr, pfn, old_pfn;
pgprot_t old_prot, new_prot, req_prot;
- int i, do_split = 1;
+ pte_t new_pte, old_pte, *tmp;
enum pg_level level;
+ int i;

- if (cpa->force_split)
- return 1;
-
- spin_lock(&pgd_lock);
/*
* Check for races, another CPU might have split this page
* up already:
*/
tmp = _lookup_address_cpa(cpa, address, &level);
if (tmp != kpte)
- goto out_unlock;
+ return 1;

switch (level) {
case PG_LEVEL_2M:
@@ -581,8 +576,7 @@ try_preserve_large_page(pte_t *kpte, uns
old_pfn = pud_pfn(*(pud_t *)kpte);
break;
default:
- do_split = -EINVAL;
- goto out_unlock;
+ return -EINVAL;
}

psize = page_level_size(level);
@@ -592,8 +586,8 @@ try_preserve_large_page(pte_t *kpte, uns
* Calculate the number of pages, which fit into this large
* page starting at address:
*/
- nextpage_addr = (address + psize) & pmask;
- numpages = (nextpage_addr - address) >> PAGE_SHIFT;
+ lpaddr = (address + psize) & pmask;
+ numpages = (lpaddr - address) >> PAGE_SHIFT;
if (numpages < cpa->numpages)
cpa->numpages = numpages;

@@ -620,57 +614,62 @@ try_preserve_large_page(pte_t *kpte, uns
pgprot_val(req_prot) |= _PAGE_PSE;

/*
- * old_pfn points to the large page base pfn. So we need
- * to add the offset of the virtual address:
+ * old_pfn points to the large page base pfn. So we need to add the
+ * offset of the virtual address:
*/
pfn = old_pfn + ((address & (psize - 1)) >> PAGE_SHIFT);
cpa->pfn = pfn;

- new_prot = static_protections(req_prot, address, pfn);
+ /*
+ * Calculate the large page base address and the number of 4K pages
+ * in the large page
+ */
+ lpaddr = address & pmask;
+ numpages = psize >> PAGE_SHIFT;

/*
- * We need to check the full range, whether
- * static_protection() requires a different pgprot for one of
- * the pages in the range we try to preserve:
+ * Make sure that the requested pgprot does not violate the static
+ * protections. Check the full large page whether one of the pages
+ * in it results in a different pgprot than the first one of the
+ * requested range. If yes, then the page needs to be split.
*/
- addr = address & pmask;
+ new_prot = static_protections(req_prot, address, pfn);
pfn = old_pfn;
- for (i = 0; i < (psize >> PAGE_SHIFT); i++, addr += PAGE_SIZE, pfn++) {
+ for (i = 0, addr = lpaddr; i < numpages; 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;
+ return 1;
}

- /*
- * If there are no changes, return. maxpages has been updated
- * above:
- */
- if (pgprot_val(new_prot) == pgprot_val(old_prot)) {
- do_split = 0;
- goto out_unlock;
- }
+ /* If there are no changes, return. */
+ if (pgprot_val(new_prot) == pgprot_val(old_prot))
+ return 0;

/*
- * We need to change the attributes. Check, whether we can
- * change the large page in one go. We request a split, when
- * the address is not aligned and the number of pages is
- * smaller than the number of pages in the large page. Note
- * that we limited the number of possible pages already to
- * the number of pages in the large page.
+ * Verify that the address is aligned and the number of pages
+ * covers the full page.
*/
- if (address == (address & pmask) && cpa->numpages == (psize >> PAGE_SHIFT)) {
- /*
- * The address is aligned and the number of pages
- * covers the full page.
- */
- new_pte = pfn_pte(old_pfn, new_prot);
- __set_pmd_pte(kpte, address, new_pte);
- cpa->flags |= CPA_FLUSHTLB;
- do_split = 0;
- }
+ if (address != lpaddr || cpa->numpages != numpages)
+ return 1;
+
+ /* All checks passed. Update the large page mapping. */
+ new_pte = pfn_pte(old_pfn, new_prot);
+ __set_pmd_pte(kpte, address, new_pte);
+ cpa->flags |= CPA_FLUSHTLB;
+ return 0;
+}

-out_unlock:
+static int should_split_large_page(pte_t *kpte, unsigned long address,
+ struct cpa_data *cpa)
+{
+ int do_split;
+
+ if (cpa->force_split)
+ return 1;
+
+ spin_lock(&pgd_lock);
+ do_split = __should_split_large_page(kpte, address, cpa);
spin_unlock(&pgd_lock);

return do_split;
@@ -1273,7 +1272,7 @@ static int __change_page_attr(struct cpa
* Check, whether we can keep the large page intact
* and just change the pte:
*/
- do_split = try_preserve_large_page(kpte, address, cpa);
+ do_split = should_split_large_page(kpte, address, cpa);
/*
* When the range fits into the existing large page,
* return. cp->numpages and cpa->tlbflush have been updated in
@@ -1288,23 +1287,23 @@ static int __change_page_attr(struct cpa
err = split_large_page(cpa, kpte, address);
if (!err) {
/*
- * Do a global flush tlb after splitting the large page
- * and before we do the actual change page attribute in the PTE.
- *
- * With out this, we violate the TLB application note, that says
- * "The TLBs may contain both ordinary and large-page
+ * Do a global flush tlb after splitting the large page
+ * and before we do the actual change page attribute in the PTE.
+ *
+ * With out this, we violate the TLB application note, that says
+ * "The TLBs may contain both ordinary and large-page
* translations for a 4-KByte range of linear addresses. This
* may occur if software modifies the paging structures so that
* the page size used for the address range changes. If the two
* translations differ with respect to page frame or attributes
* (e.g., permissions), processor behavior is undefined and may
* be implementation-specific."
- *
- * We do this global tlb flush inside the cpa_lock, so that we
+ *
+ * We do this global tlb flush inside the cpa_lock, so that we
* don't allow any other cpu, with stale tlb entries change the
* page attribute in parallel, that also falls into the
* just split large page entry.
- */
+ */
flush_tlb_all();
goto repeat;
}