KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 204 insertions, 0 deletions

diff --git a/arch/arm/mm/cache-v4wt.S b/arch/arm/mm/cache-v4wt.S
new file mode 100644
index 000000000..2ee62e4b2
--- /dev/null
+++ b/arch/arm/mm/cache-v4wt.S
@@ -0,0 +1,204 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/arch/arm/mm/cache-v4wt.S
+ *
+ *  Copyright (C) 1997-2002 Russell king
+ *
+ *  ARMv4 write through cache operations support.
+ *
+ *  We assume that the write buffer is not enabled.
+ */
+#include <linux/linkage.h>
+#include <linux/init.h>
+#include <linux/cfi_types.h>
+#include <asm/assembler.h>
+#include <asm/page.h>
+#include "proc-macros.S"
+
+/*
+ * The size of one data cache line.
+ */
+#define CACHE_DLINESIZE	32
+
+/*
+ * The number of data cache segments.
+ */
+#define CACHE_DSEGMENTS	8
+
+/*
+ * The number of lines in a cache segment.
+ */
+#define CACHE_DENTRIES	64
+
+/*
+ * This is the size at which it becomes more efficient to
+ * clean the whole cache, rather than using the individual
+ * cache line maintenance instructions.
+ *
+ * *** This needs benchmarking
+ */
+#define CACHE_DLIMIT	16384
+
+/*
+ *	flush_icache_all()
+ *
+ *	Unconditionally clean and invalidate the entire icache.
+ */
+SYM_TYPED_FUNC_START(v4wt_flush_icache_all)
+	mov	r0, #0
+	mcr	p15, 0, r0, c7, c5, 0		@ invalidate I cache
+	ret	lr
+SYM_FUNC_END(v4wt_flush_icache_all)
+
+/*
+ *	flush_user_cache_all()
+ *
+ *	Invalidate all cache entries in a particular address
+ *	space.
+ */
+SYM_FUNC_ALIAS(v4wt_flush_user_cache_all, v4wt_flush_kern_cache_all)
+
+/*
+ *	flush_kern_cache_all()
+ *
+ *	Clean and invalidate the entire cache.
+ */
+SYM_TYPED_FUNC_START(v4wt_flush_kern_cache_all)
+	mov	r2, #VM_EXEC
+	mov	ip, #0
+__flush_whole_cache:
+	tst	r2, #VM_EXEC
+	mcrne	p15, 0, ip, c7, c5, 0		@ invalidate I cache
+	mcr	p15, 0, ip, c7, c6, 0		@ invalidate D cache
+	ret	lr
+SYM_FUNC_END(v4wt_flush_kern_cache_all)
+
+/*
+ *	flush_user_cache_range(start, end, flags)
+ *
+ *	Clean and invalidate a range of cache entries in the specified
+ *	address space.
+ *
+ *	- start - start address (inclusive, page aligned)
+ *	- end	- end address (exclusive, page aligned)
+ *	- flags	- vma_area_struct flags describing address space
+ */
+SYM_TYPED_FUNC_START(v4wt_flush_user_cache_range)
+	sub	r3, r1, r0			@ calculate total size
+	cmp	r3, #CACHE_DLIMIT
+	bhs	__flush_whole_cache
+
+1:	mcr	p15, 0, r0, c7, c6, 1		@ invalidate D entry
+	tst	r2, #VM_EXEC
+	mcrne	p15, 0, r0, c7, c5, 1		@ invalidate I entry
+	add	r0, r0, #CACHE_DLINESIZE
+	cmp	r0, r1
+	blo	1b
+	ret	lr
+SYM_FUNC_END(v4wt_flush_user_cache_range)
+
+/*
+ *	coherent_kern_range(start, end)
+ *
+ *	Ensure coherency between the Icache and the Dcache in the
+ *	region described by start.  If you have non-snooping
+ *	Harvard caches, you need to implement this function.
+ *
+ *	- start  - virtual start address
+ *	- end	 - virtual end address
+ */
+SYM_TYPED_FUNC_START(v4wt_coherent_kern_range)
+#ifdef CONFIG_CFI /* Fallthrough if !CFI */
+	b	v4wt_coherent_user_range
+#endif
+SYM_FUNC_END(v4wt_coherent_kern_range)
+
+/*
+ *	coherent_user_range(start, end)
+ *
+ *	Ensure coherency between the Icache and the Dcache in the
+ *	region described by start.  If you have non-snooping
+ *	Harvard caches, you need to implement this function.
+ *
+ *	- start  - virtual start address
+ *	- end	 - virtual end address
+ */
+SYM_TYPED_FUNC_START(v4wt_coherent_user_range)
+	bic	r0, r0, #CACHE_DLINESIZE - 1
+1:	mcr	p15, 0, r0, c7, c5, 1		@ invalidate I entry
+	add	r0, r0, #CACHE_DLINESIZE
+	cmp	r0, r1
+	blo	1b
+	mov	r0, #0
+	ret	lr
+SYM_FUNC_END(v4wt_coherent_user_range)
+
+/*
+ *	flush_kern_dcache_area(void *addr, size_t size)
+ *
+ *	Ensure no D cache aliasing occurs, either with itself or
+ *	the I cache
+ *
+ *	- addr	- kernel address
+ *	- size	- region size
+ */
+SYM_TYPED_FUNC_START(v4wt_flush_kern_dcache_area)
+	mov	r2, #0
+	mcr	p15, 0, r2, c7, c5, 0		@ invalidate I cache
+	add	r1, r0, r1
+	b	v4wt_dma_inv_range
+SYM_FUNC_END(v4wt_flush_kern_dcache_area)
+
+/*
+ *	dma_inv_range(start, end)
+ *
+ *	Invalidate (discard) the specified virtual address range.
+ *	May not write back any entries.  If 'start' or 'end'
+ *	are not cache line aligned, those lines must be written
+ *	back.
+ *
+ *	- start  - virtual start address
+ *	- end	 - virtual end address
+ */
+v4wt_dma_inv_range:
+	bic	r0, r0, #CACHE_DLINESIZE - 1
+1:	mcr	p15, 0, r0, c7, c6, 1		@ invalidate D entry
+	add	r0, r0, #CACHE_DLINESIZE
+	cmp	r0, r1
+	blo	1b
+	ret	lr
+
+/*
+ *	dma_flush_range(start, end)
+ *
+ *	Clean and invalidate the specified virtual address range.
+ *
+ *	- start  - virtual start address
+ *	- end	 - virtual end address
+*/
+SYM_TYPED_FUNC_START(v4wt_dma_flush_range)
+	b	v4wt_dma_inv_range
+SYM_FUNC_END(v4wt_dma_flush_range)
+
+/*
+ *	dma_unmap_area(start, size, dir)
+ *	- start	- kernel virtual start address
+ *	- size	- size of region
+ *	- dir	- DMA direction
+ */
+SYM_TYPED_FUNC_START(v4wt_dma_unmap_area)
+	add	r1, r1, r0
+	teq	r2, #DMA_TO_DEVICE
+	bne	v4wt_dma_inv_range
+	ret	lr
+SYM_FUNC_END(v4wt_dma_unmap_area)
+
+/*
+ *	dma_map_area(start, size, dir)
+ *	- start	- kernel virtual start address
+ *	- size	- size of region
+ *	- dir	- DMA direction
+ */
+SYM_TYPED_FUNC_START(v4wt_dma_map_area)
+	ret	lr
+SYM_FUNC_END(v4wt_dma_map_area)