powerpc fixes for 5.2 #4

One fix for a regression introduced by our 32-bit KASAN support, which broke
 booting on machines with "bootx" early debugging enabled.
 
 A fix for a bug which broke kexec on 32-bit, introduced by changes to the 32-bit
 STRICT_KERNEL_RWX support in v5.1.
 
 Finally two fixes going to stable for our THP split/collapse handling,
 discovered by Nick. The first fixes random crashes and/or corruption in guests
 under sufficient load.
 
 Thanks to:
   Nicholas Piggin, Christophe Leroy, Aaro Koskinen, Mathieu Malaterre.
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Merge tag 'powerpc-5.2-4' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux

Pull powerpc fixes from Michael Ellerman:
 "One fix for a regression introduced by our 32-bit KASAN support, which
  broke booting on machines with "bootx" early debugging enabled.

  A fix for a bug which broke kexec on 32-bit, introduced by changes to
  the 32-bit STRICT_KERNEL_RWX support in v5.1.

  Finally two fixes going to stable for our THP split/collapse handling,
  discovered by Nick. The first fixes random crashes and/or corruption
  in guests under sufficient load.

  Thanks to: Nicholas Piggin, Christophe Leroy, Aaro Koskinen, Mathieu
  Malaterre"

* tag 'powerpc-5.2-4' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  powerpc/32s: fix booting with CONFIG_PPC_EARLY_DEBUG_BOOTX
  powerpc/64s: __find_linux_pte() synchronization vs pmdp_invalidate()
  powerpc/64s: Fix THP PMD collapse serialisation
  powerpc: Fix kexec failure on book3s/32

arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -876,6 +876,23 @@ static inline int pmd_present(pmd_t pmd)
 	return false;
 }
 
+static inline int pmd_is_serializing(pmd_t pmd)
+{
+	/*
+	 * If the pmd is undergoing a split, the _PAGE_PRESENT bit is clear
+	 * and _PAGE_INVALID is set (see pmd_present, pmdp_invalidate).
+	 *
+	 * This condition may also occur when flushing a pmd while flushing
+	 * it (see ptep_modify_prot_start), so callers must ensure this
+	 * case is fine as well.
+	 */
+	if ((pmd_raw(pmd) & cpu_to_be64(_PAGE_PRESENT | _PAGE_INVALID)) ==
+						cpu_to_be64(_PAGE_INVALID))
+		return true;
+
+	return false;
+}
+
 static inline int pmd_bad(pmd_t pmd)
 {
 	if (radix_enabled())
@@ -1092,6 +1109,19 @@ static inline int pmd_protnone(pmd_t pmd)
 #define pmd_access_permitted pmd_access_permitted
 static inline bool pmd_access_permitted(pmd_t pmd, bool write)
 {
+	/*
+	 * pmdp_invalidate sets this combination (which is not caught by
+	 * !pte_present() check in pte_access_permitted), to prevent
+	 * lock-free lookups, as part of the serialize_against_pte_lookup()
+	 * synchronisation.
+	 *
+	 * This also catches the case where the PTE's hardware PRESENT bit is
+	 * cleared while TLB is flushed, which is suboptimal but should not
+	 * be frequent.
+	 */
+	if (pmd_is_serializing(pmd))
+		return false;
+
 	return pte_access_permitted(pmd_pte(pmd), write);
 }
 

arch/powerpc/include/asm/btext.h

@@ -13,7 +13,11 @@ extern void btext_update_display(unsigned long phys, int width, int height,
 				 int depth, int pitch);
 extern void btext_setup_display(int width, int height, int depth, int pitch,
 				unsigned long address);
+#ifdef CONFIG_PPC32
 extern void btext_prepare_BAT(void);
+#else
+static inline void btext_prepare_BAT(void) { }
+#endif
 extern void btext_map(void);
 extern void btext_unmap(void);
 

arch/powerpc/include/asm/kexec.h

@@ -94,6 +94,9 @@ static inline bool kdump_in_progress(void)
 	return crashing_cpu >= 0;
 }
 
+void relocate_new_kernel(unsigned long indirection_page, unsigned long reboot_code_buffer,
+			 unsigned long start_address) __noreturn;
+
 #ifdef CONFIG_KEXEC_FILE
 extern const struct kexec_file_ops kexec_elf64_ops;
 

arch/powerpc/kernel/machine_kexec_32.c

@@ -30,7 +30,6 @@ typedef void (*relocate_new_kernel_t)(
  */
 void default_machine_kexec(struct kimage *image)
 {
-	extern const unsigned char relocate_new_kernel[];
 	extern const unsigned int relocate_new_kernel_size;
 	unsigned long page_list;
 	unsigned long reboot_code_buffer, reboot_code_buffer_phys;
@@ -58,6 +57,9 @@ void default_machine_kexec(struct kimage *image)
 				reboot_code_buffer + KEXEC_CONTROL_PAGE_SIZE);
 	printk(KERN_INFO "Bye!\n");
 
+	if (!IS_ENABLED(CONFIG_FSL_BOOKE) && !IS_ENABLED(CONFIG_44x))
+		relocate_new_kernel(page_list, reboot_code_buffer_phys, image->start);
+
 	/* now call it */
 	rnk = (relocate_new_kernel_t) reboot_code_buffer;
 	(*rnk)(page_list, reboot_code_buffer_phys, image->start);

arch/powerpc/kernel/prom_init.c

@@ -2336,6 +2336,7 @@ static void __init prom_check_displays(void)
 			prom_printf("W=%d H=%d LB=%d addr=0x%x\n",
 				    width, height, pitch, addr);
 			btext_setup_display(width, height, 8, pitch, addr);
+			btext_prepare_BAT();
 		}
 #endif /* CONFIG_PPC_EARLY_DEBUG_BOOTX */
 	}

arch/powerpc/kernel/prom_init_check.sh

@@ -24,7 +24,7 @@ fi
 WHITELIST="add_reloc_offset __bss_start __bss_stop copy_and_flush
 _end enter_prom $MEM_FUNCS reloc_offset __secondary_hold
 __secondary_hold_acknowledge __secondary_hold_spinloop __start
-logo_linux_clut224
+logo_linux_clut224 btext_prepare_BAT
 reloc_got2 kernstart_addr memstart_addr linux_banner _stext
 __prom_init_toc_start __prom_init_toc_end btext_setup_display TOC."
 

arch/powerpc/mm/book3s64/pgtable.c

@@ -112,6 +112,9 @@ pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
 	/*
 	 * This ensures that generic code that rely on IRQ disabling
 	 * to prevent a parallel THP split work as expected.
+	 *
+	 * Marking the entry with _PAGE_INVALID && ~_PAGE_PRESENT requires
+	 * a special case check in pmd_access_permitted.
 	 */
 	serialize_against_pte_lookup(vma->vm_mm);
 	return __pmd(old_pmd);

arch/powerpc/mm/pgtable.c

@@ -368,13 +368,25 @@ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea,
 	pdshift = PMD_SHIFT;
 	pmdp = pmd_offset(&pud, ea);
 	pmd  = READ_ONCE(*pmdp);
+
 	/*
-	 * A hugepage collapse is captured by pmd_none, because
-	 * it mark the pmd none and do a hpte invalidate.
+	 * A hugepage collapse is captured by this condition, see
+	 * pmdp_collapse_flush.
 	 */
 	if (pmd_none(pmd))
 		return NULL;
 
+#ifdef CONFIG_PPC_BOOK3S_64
+	/*
+	 * A hugepage split is captured by this condition, see
+	 * pmdp_invalidate.
+	 *
+	 * Huge page modification can be caught here too.
+	 */
+	if (pmd_is_serializing(pmd))
+		return NULL;
+#endif
+
 	if (pmd_trans_huge(pmd) || pmd_devmap(pmd)) {
 		if (is_thp)
 			*is_thp = true;