Re: [PATCH v3 2/2] powerpc: Add set_memory_{p/np}() and remove set_memory_attr()

set_memory_attr() was implemented by commit 4d1755b6a762 ("powerpc/mm:
implement set_memory_attr()") because the set_memory_xx() couldn't
be used at that time to modify memory "on the fly" as explained it
the commit.

But set_memory_attr() uses set_pte_at() which leads to warnings when
CONFIG_DEBUG_VM is selected, because set_pte_at() is unexpected for
updating existing page table entries.

The check could be bypassed by using __set_pte_at() instead,
as it was the case before commit c988cfd38e48 ("powerpc/32:
use set_memory_attr()") but since commit 9f7853d7609d ("powerpc/mm:
Fix set_memory_*() against concurrent accesses") it is now possible
to use set_memory_xx() functions to update page table entries
"on the fly" because the update is now atomic.

For DEBUG_PAGEALLOC we need to clear and set back _PAGE_PRESENT.
Add set_memory_np() and set_memory_p() for that.

Replace all uses of set_memory_attr() by the relevant set_memory_xx()
and remove set_memory_attr().

Reported-by: Maxime Bizon <redacted>
Fixes: c988cfd38e48 ("powerpc/32: use set_memory_attr()")
Cc: stable@vger.kernel.org
Depends-on: 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against concurrent accesses")
Signed-off-by: Christophe Leroy <redacted>
Reviewed-by: Russell Currey <redacted>
Tested-by: Maxime Bizon <redacted>
---
v3: Use _PAGE_PRESENT directly as all platforms have the bit

v2: Add comment to SET_MEMORY_P and SET_MEMORY_NP
---
  arch/powerpc/include/asm/set_memory.h | 12 ++++++++-
  arch/powerpc/mm/pageattr.c            | 39 +++++----------------------
  arch/powerpc/mm/pgtable_32.c          | 24 ++++++++---------
  3 files changed, 28 insertions(+), 47 deletions(-)

diff --git a/arch/powerpc/include/asm/set_memory.h b/arch/powerpc/include/asm/set_memory.h
index b040094f7920..7ebc807aa8cc 100644
--- a/arch/powerpc/include/asm/set_memory.h
+++ b/arch/powerpc/include/asm/set_memory.h

@@ -6,6 +6,8 @@
  #define SET_MEMORY_RW	1
  #define SET_MEMORY_NX	2
  #define SET_MEMORY_X	3
+#define SET_MEMORY_NP	4	/* Set memory non present */
+#define SET_MEMORY_P	5	/* Set memory present */
  
  int change_memory_attr(unsigned long addr, int numpages, long action);
  

@@ -29,6 +31,14 @@ static inline int set_memory_x(unsigned long addr, int numpages)
  	return change_memory_attr(addr, numpages, SET_MEMORY_X);
  }
  
-int set_memory_attr(unsigned long addr, int numpages, pgprot_t prot);
+static inline int set_memory_np(unsigned long addr, int numpages)
+{
+	return change_memory_attr(addr, numpages, SET_MEMORY_NP);
+}
+
+static inline int set_memory_p(unsigned long addr, int numpages)
+{
+	return change_memory_attr(addr, numpages, SET_MEMORY_P);
+}
  
  #endif

diff --git a/arch/powerpc/mm/pageattr.c b/arch/powerpc/mm/pageattr.c
index 8812454e70ff..85753e32a4de 100644
--- a/arch/powerpc/mm/pageattr.c
+++ b/arch/powerpc/mm/pageattr.c

@@ -46,6 +46,12 @@ static int change_page_attr(pte_t *ptep, unsigned long addr, void *data)
  	case SET_MEMORY_X:
  		pte_update_delta(ptep, addr, _PAGE_KERNEL_RO, _PAGE_KERNEL_ROX);
  		break;
+	case SET_MEMORY_NP:
+		pte_update(&init_mm, addr, ptep, _PAGE_PRESENT, 0, 0);
+		break;
+	case SET_MEMORY_P:
+		pte_update(&init_mm, addr, ptep, 0, _PAGE_PRESENT, 0);
+		break;
  	default:
  		WARN_ON_ONCE(1);
  		break;

@@ -90,36 +96,3 @@ int change_memory_attr(unsigned long addr, int numpages, long action)
  	return apply_to_existing_page_range(&init_mm, start, size,
  					    change_page_attr, (void *)action);
  }
-
-/*
- * Set the attributes of a page:
- *
- * This function is used by PPC32 at the end of init to set final kernel memory
- * protection. It includes changing the maping of the page it is executing from
- * and data pages it is using.
- */
-static int set_page_attr(pte_t *ptep, unsigned long addr, void *data)
-{
-	pgprot_t prot = __pgprot((unsigned long)data);
-
-	spin_lock(&init_mm.page_table_lock);
-
-	set_pte_at(&init_mm, addr, ptep, pte_modify(*ptep, prot));
-	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
-
-	spin_unlock(&init_mm.page_table_lock);
-
-	return 0;
-}
-
-int set_memory_attr(unsigned long addr, int numpages, pgprot_t prot)
-{
-	unsigned long start = ALIGN_DOWN(addr, PAGE_SIZE);
-	unsigned long sz = numpages * PAGE_SIZE;
-
-	if (numpages <= 0)
-		return 0;
-
-	return apply_to_existing_page_range(&init_mm, start, sz, set_page_attr,
-					    (void *)pgprot_val(prot));
-}

diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index 906e4e4328b2..f71ededdc02a 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c

@@ -135,10 +135,12 @@ void mark_initmem_nx(void)
  	unsigned long numpages = PFN_UP((unsigned long)_einittext) -
  				 PFN_DOWN((unsigned long)_sinittext);
  
-	if (v_block_mapped((unsigned long)_sinittext))
+	if (v_block_mapped((unsigned long)_sinittext)) {
  		mmu_mark_initmem_nx();
-	else
-		set_memory_attr((unsigned long)_sinittext, numpages, PAGE_KERNEL);
+	} else {
+		set_memory_nx((unsigned long)_sinittext, numpages);
+		set_memory_rw((unsigned long)_sinittext, numpages);
+	}
  }
  
  #ifdef CONFIG_STRICT_KERNEL_RWX

@@ -152,18 +154,14 @@ void mark_rodata_ro(void)
  		return;
  	}
  
-	numpages = PFN_UP((unsigned long)_etext) -
-		   PFN_DOWN((unsigned long)_stext);
-
-	set_memory_attr((unsigned long)_stext, numpages, PAGE_KERNEL_ROX);
  	/*
-	 * mark .rodata as read only. Use __init_begin rather than __end_rodata
-	 * to cover NOTES and EXCEPTION_TABLE.
+	 * mark .text and .rodata as read only. Use __init_begin rather than
+	 * __end_rodata to cover NOTES and EXCEPTION_TABLE.
  	 */
  	numpages = PFN_UP((unsigned long)__init_begin) -
-		   PFN_DOWN((unsigned long)__start_rodata);
+		   PFN_DOWN((unsigned long)_stext);
  
-	set_memory_attr((unsigned long)__start_rodata, numpages, PAGE_KERNEL_RO);
+	set_memory_ro((unsigned long)_stext, numpages);
  
  	// mark_initmem_nx() should have already run by now
  	ptdump_check_wx();

@@ -179,8 +177,8 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
  		return;
  
  	if (enable)
-		set_memory_attr(addr, numpages, PAGE_KERNEL);
+		set_memory_p(addr, numpages);
  	else
-		set_memory_attr(addr, numpages, __pgprot(0));
+		set_memory_np(addr, numpages);
  }
  #endif /* CONFIG_DEBUG_PAGEALLOC */