arm64: kill flush_cache_all()

The documented semantics of flush_cache_all are not possible to provide
for arm64 (short of flushing the entire physical address space by VA),
and there are currently no users; KVM uses VA maintenance exclusively,
cpu_reset is never called, and the only two users outside of arch code
cannot be built for arm64.

While cpu_soft_reset and related functions (which call flush_cache_all)
were thought to be useful for kexec, their current implementations only
serve to mask bugs. For correctness kexec will need to perform
maintenance by VA anyway to account for system caches, line migration,
and other subtleties of the cache architecture. As the extent of this
cache maintenance will be kexec-specific, it should probably live in the
kexec code.

This patch removes flush_cache_all, and related unused components,
preventing further abuse.

Signed-off-by: Mark Rutland <[email protected]>
Cc: AKASHI Takahiro <[email protected]>
Cc: Geoff Levand <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Acked-by: Lorenzo Pieralisi <[email protected]>
Acked-by: Marc Zyngier <[email protected]>
Acked-by: Will Deacon <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>

Author: mrutland-arm

arch/arm64/include/asm/cacheflush.h

@@ -40,10 +40,6 @@
  *	the implementation assumes non-aliasing VIPT D-cache and (aliasing)
  *	VIPT or ASID-tagged VIVT I-cache.
  *
- *	flush_cache_all()
- *
- *		Unconditionally clean and invalidate the entire cache.
- *
  *	flush_cache_mm(mm)
  *
  *		Clean and invalidate all user space cache entries
@@ -69,7 +65,6 @@
  *		- kaddr  - page address
  *		- size   - region size
  */
-extern void flush_cache_all(void);
 extern void flush_cache_range(struct vm_area_struct *vma, unsigned long start, unsigned long end);
 extern void flush_icache_range(unsigned long start, unsigned long end);
 extern void __flush_dcache_area(void *addr, size_t len);

arch/arm64/include/asm/proc-fns.h

@@ -28,12 +28,8 @@
 struct mm_struct;
 struct cpu_suspend_ctx;
 
-extern void cpu_cache_off(void);
 extern void cpu_do_idle(void);
 extern void cpu_do_switch_mm(unsigned long pgd_phys, struct mm_struct *mm);
-extern void cpu_reset(unsigned long addr) __attribute__((noreturn));
-void cpu_soft_restart(phys_addr_t cpu_reset,
-		unsigned long addr) __attribute__((noreturn));
 extern void cpu_do_suspend(struct cpu_suspend_ctx *ptr);
 extern u64 cpu_do_resume(phys_addr_t ptr, u64 idmap_ttbr);
 

arch/arm64/include/asm/system_misc.h

@@ -41,7 +41,6 @@ struct mm_struct;
 extern void show_pte(struct mm_struct *mm, unsigned long addr);
 extern void __show_regs(struct pt_regs *);
 
-void soft_restart(unsigned long);
 extern void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
 
 #define UDBG_UNDEFINED	(1 << 0)

arch/arm64/kernel/process.c

@@ -58,14 +58,6 @@ unsigned long __stack_chk_guard __read_mostly;
 EXPORT_SYMBOL(__stack_chk_guard);
 #endif
 
-void soft_restart(unsigned long addr)
-{
-	setup_mm_for_reboot();
-	cpu_soft_restart(virt_to_phys(cpu_reset), addr);
-	/* Should never get here */
-	BUG();
-}
-
 /*
  * Function pointers to optional machine specific functions
  */
@@ -136,9 +128,7 @@ void machine_power_off(void)
 
 /*
  * Restart requires that the secondary CPUs stop performing any activity
- * while the primary CPU resets the system. Systems with a single CPU can
- * use soft_restart() as their machine descriptor's .restart hook, since that
- * will cause the only available CPU to reset. Systems with multiple CPUs must
+ * while the primary CPU resets the system. Systems with multiple CPUs must
  * provide a HW restart implementation, to ensure that all CPUs reset at once.
  * This is required so that any code running after reset on the primary CPU
  * doesn't have to co-ordinate with other CPUs to ensure they aren't still

arch/arm64/mm/cache.S

@@ -26,79 +26,6 @@
 
 #include "proc-macros.S"
 
-/*
- *	__flush_dcache_all()
- *
- *	Flush the whole D-cache.
- *
- *	Corrupted registers: x0-x7, x9-x11
- */
-__flush_dcache_all:
-	dmb	sy				// ensure ordering with previous memory accesses
-	mrs	x0, clidr_el1			// read clidr
-	and	x3, x0, #0x7000000		// extract loc from clidr
-	lsr	x3, x3, #23			// left align loc bit field
-	cbz	x3, finished			// if loc is 0, then no need to clean
-	mov	x10, #0				// start clean at cache level 0
-loop1:
-	add	x2, x10, x10, lsr #1		// work out 3x current cache level
-	lsr	x1, x0, x2			// extract cache type bits from clidr
-	and	x1, x1, #7			// mask of the bits for current cache only
-	cmp	x1, #2				// see what cache we have at this level
-	b.lt	skip				// skip if no cache, or just i-cache
-	save_and_disable_irqs x9		// make CSSELR and CCSIDR access atomic
-	msr	csselr_el1, x10			// select current cache level in csselr
-	isb					// isb to sych the new cssr&csidr
-	mrs	x1, ccsidr_el1			// read the new ccsidr
-	restore_irqs x9
-	and	x2, x1, #7			// extract the length of the cache lines
-	add	x2, x2, #4			// add 4 (line length offset)
-	mov	x4, #0x3ff
-	and	x4, x4, x1, lsr #3		// find maximum number on the way size
-	clz	w5, w4				// find bit position of way size increment
-	mov	x7, #0x7fff
-	and	x7, x7, x1, lsr #13		// extract max number of the index size
-loop2:
-	mov	x9, x4				// create working copy of max way size
-loop3:
-	lsl	x6, x9, x5
-	orr	x11, x10, x6			// factor way and cache number into x11
-	lsl	x6, x7, x2
-	orr	x11, x11, x6			// factor index number into x11
-	dc	cisw, x11			// clean & invalidate by set/way
-	subs	x9, x9, #1			// decrement the way
-	b.ge	loop3
-	subs	x7, x7, #1			// decrement the index
-	b.ge	loop2
-skip:
-	add	x10, x10, #2			// increment cache number
-	cmp	x3, x10
-	b.gt	loop1
-finished:
-	mov	x10, #0				// swith back to cache level 0
-	msr	csselr_el1, x10			// select current cache level in csselr
-	dsb	sy
-	isb
-	ret
-ENDPROC(__flush_dcache_all)
-
-/*
- *	flush_cache_all()
- *
- *	Flush the entire cache system.  The data cache flush is now achieved
- *	using atomic clean / invalidates working outwards from L1 cache. This
- *	is done using Set/Way based cache maintainance instructions.  The
- *	instruction cache can still be invalidated back to the point of
- *	unification in a single instruction.
- */
-ENTRY(flush_cache_all)
-	mov	x12, lr
-	bl	__flush_dcache_all
-	mov	x0, #0
-	ic	ialluis				// I+BTB cache invalidate
-	ret	x12
-ENDPROC(flush_cache_all)
-
 /*
  *	flush_icache_range(start,end)
  *

arch/arm64/mm/flush.c

@@ -102,7 +102,6 @@ EXPORT_SYMBOL(flush_dcache_page);
 /*
  * Additional functions defined in assembly.
  */
-EXPORT_SYMBOL(flush_cache_all);
 EXPORT_SYMBOL(flush_icache_range);
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE

arch/arm64/mm/proc.S

@@ -45,52 +45,6 @@
 
 #define MAIR(attr, mt)	((attr) << ((mt) * 8))
 
-/*
- *	cpu_cache_off()
- *
- *	Turn the CPU D-cache off.
- */
-ENTRY(cpu_cache_off)
-	mrs	x0, sctlr_el1
-	bic	x0, x0, #1 << 2			// clear SCTLR.C
-	msr	sctlr_el1, x0
-	isb
-	ret
-ENDPROC(cpu_cache_off)
-
-/*
- *	cpu_reset(loc)
- *
- *	Perform a soft reset of the system.  Put the CPU into the same state
- *	as it would be if it had been reset, and branch to what would be the
- *	reset vector. It must be executed with the flat identity mapping.
- *
- *	- loc   - location to jump to for soft reset
- */
-	.align	5
-ENTRY(cpu_reset)
-	mrs	x1, sctlr_el1
-	bic	x1, x1, #1
-	msr	sctlr_el1, x1			// disable the MMU
-	isb
-	ret	x0
-ENDPROC(cpu_reset)
-
-ENTRY(cpu_soft_restart)
-	/* Save address of cpu_reset() and reset address */
-	mov	x19, x0
-	mov	x20, x1
-
-	/* Turn D-cache off */
-	bl	cpu_cache_off
-
-	/* Push out all dirty data, and ensure cache is empty */
-	bl	flush_cache_all
-
-	mov	x0, x20
-	ret	x19
-ENDPROC(cpu_soft_restart)
-
 /*
  *	cpu_do_idle()
  *