RISC-V Fixes for 5.0-rc7

This tag contains a pair of bug fixes that I'd like to include in 5.0:
 
 * A fix to disambiguate swap from invalid PTEs, which fixes an error
   when trying to unmap PROT_NONE pages.
 * A revert to an optimization of the size of flat binaries.  This is
   really a workaround to prevent breaking existing boot flows, but since
   the change was introduced as part of the 5.0 merge window I'd like to
   have the fix in before 5.0 so we can avoid a regression for any proper
   releases.
 
 With these I hope we're out of patches for 5.0 in RISC-V land.
 -----BEGIN PGP SIGNATURE-----
 
 iQJHBAABCAAxFiEEAM520YNJYN/OiG3470yhUCzLq0EFAlxjN2gTHHBhbG1lckBk
 YWJiZWx0LmNvbQAKCRDvTKFQLMurQY73EACOoplTb4zBKXY4pCSZG/Gnu+AEJz77
 CS1wR86TThkyxIJTlIGmX0xSFuds4f+ymCMbZ7SfXa20es62iZtEQA72TVb+g80L
 hD/0yZFZQkcBEQOVOC2ZWvaj4tVZB703yHYZGSnN/6sHISS0yoO8fqf19SGSmDC3
 aCNE5Fm6z5MNozS6Z5Lrtpw2rmpDwQCHnxfLPzEvjC9DPMwzHQbyP3tALWcfLpK7
 aIPmq/xjUtS5eVb/3CHhLmkYFTNlOs4p0jsKjw2Sw/3NWHCXrPw6afrjZ533j8nR
 BI/u/EErMJWl6qLasdzTTfhE16sLDzbowiGdOfSurjwRDkAokw9/zvLDLDzLXwoT
 UQkCcp2mnOsCmdXaC8L0yUi3mHh2M82GL1RXq4POyCgD77DqVvAJ/ot/Lq3UFila
 T2rfsxIFC2pHmdDlQe1zo31g6TeI4FJaHA4juNXce2bIbtaU4OxqiXfN/cKjyAX2
 8hevxUwy/PY0aqzLl14Xg2tcdurVbFh8BZ7eWYwqWsTrVwRg0ZhnWG0FdopNMA9D
 z5nBbE3KnVEDrMh7QzSgtNDzSmWRUKD0S5B0t4/lMv9uvYrtqeBXCKS3vJ1tc0zy
 tzj+tyjmgsfkAIVfA/fQqznx7sXAdD/jCPkUtotQUP2YkKRFbVyLjVTXKQ3BiyAl
 xrZhsMPr8BPj0Q==
 =EjWP
 -----END PGP SIGNATURE-----

Merge tag 'riscv-for-linus-5.0-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux

Pull RISC-V fixes from Palmer Dabbelt:
 "This contains a pair of bug fixes that I'd like to include in 5.0:

   - A fix to disambiguate swap from invalid PTEs, which fixes an error
     when trying to unmap PROT_NONE pages.

   - A revert to an optimization of the size of flat binaries. This is
     really a workaround to prevent breaking existing boot flows, but
     since the change was introduced as part of the 5.0 merge window I'd
     like to have the fix in before 5.0 so we can avoid a regression for
     any proper releases.

  With these I hope we're out of patches for 5.0 in RISC-V land"

* tag 'riscv-for-linus-5.0-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux:
  Revert "RISC-V: Make BSS section as the last section in vmlinux.lds.S"
  riscv: Add pte bit to distinguish swap from invalid

arch/riscv/include/asm/pgtable-bits.h

@@ -35,6 +35,12 @@
 #define _PAGE_SPECIAL   _PAGE_SOFT
 #define _PAGE_TABLE     _PAGE_PRESENT
 
+/*
+ * _PAGE_PROT_NONE is set on not-present pages (and ignored by the hardware) to
+ * distinguish them from swapped out pages
+ */
+#define _PAGE_PROT_NONE _PAGE_READ
+
 #define _PAGE_PFN_SHIFT 10
 
 /* Set of bits to preserve across pte_modify() */

arch/riscv/include/asm/pgtable.h

@@ -44,7 +44,7 @@
 /* Page protection bits */
 #define _PAGE_BASE	(_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_USER)
 
-#define PAGE_NONE		__pgprot(0)
+#define PAGE_NONE		__pgprot(_PAGE_PROT_NONE)
 #define PAGE_READ		__pgprot(_PAGE_BASE | _PAGE_READ)
 #define PAGE_WRITE		__pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_WRITE)
 #define PAGE_EXEC		__pgprot(_PAGE_BASE | _PAGE_EXEC)
@@ -98,7 +98,7 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 
 static inline int pmd_present(pmd_t pmd)
 {
-	return (pmd_val(pmd) & _PAGE_PRESENT);
+	return (pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PROT_NONE));
 }
 
 static inline int pmd_none(pmd_t pmd)
@@ -178,7 +178,7 @@ static inline pte_t *pte_offset_kernel(pmd_t *pmd, unsigned long addr)
 
 static inline int pte_present(pte_t pte)
 {
-	return (pte_val(pte) & _PAGE_PRESENT);
+	return (pte_val(pte) & (_PAGE_PRESENT | _PAGE_PROT_NONE));
 }
 
 static inline int pte_none(pte_t pte)
@@ -380,7 +380,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
  *
  * Format of swap PTE:
  *	bit            0:	_PAGE_PRESENT (zero)
- *	bit            1:	reserved for future use (zero)
+ *	bit            1:	_PAGE_PROT_NONE (zero)
  *	bits      2 to 6:	swap type
  *	bits 7 to XLEN-1:	swap offset
  */

arch/riscv/kernel/vmlinux.lds.S

@@ -18,8 +18,6 @@
 #include <asm/cache.h>
 #include <asm/thread_info.h>
 
-#define MAX_BYTES_PER_LONG	0x10
-
 OUTPUT_ARCH(riscv)
 ENTRY(_start)
 
@@ -76,6 +74,8 @@ SECTIONS
 		*(.sbss*)
 	}
 
+	BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
+
 	EXCEPTION_TABLE(0x10)
 	NOTES
 
@@ -83,10 +83,6 @@ SECTIONS
 		*(.rel.dyn*)
 	}
 
-	BSS_SECTION(MAX_BYTES_PER_LONG,
-		    MAX_BYTES_PER_LONG,
-		    MAX_BYTES_PER_LONG)
-
 	_end = .;
 
 	STABS_DEBUG