linux/arch/x86/lib/iomem.c

#include <linux/string.h>
#include <linux/module.h>
#include <linux/io.h>
#include <linux/kmsan-checks.h>

#define movs(type,to,from) \
	asm volatile("movs" type:"=&D" (to), "=&S" (from):"0" (to), "1" (from):"memory")

/* Originally from i386/string.h */
static __always_inline void rep_movs(void *to, const void *from, size_t n)
{
	unsigned long d0, d1, d2;
	asm volatile("rep ; movsl\n\t"
		     "testb $2,%b4\n\t"
		     "je 1f\n\t"
		     "movsw\n"
		     "1:\ttestb $1,%b4\n\t"
		     "je 2f\n\t"
		     "movsb\n"
		     "2:"
		     : "=&c" (d0), "=&D" (d1), "=&S" (d2)
		     : "0" (n / 4), "q" (n), "1" ((long)to), "2" ((long)from)
		     : "memory");
}

static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
{
	const void *orig_to = to;
	const size_t orig_n = n;

	if (unlikely(!n))
		return;

	/* Align any unaligned source IO */
	if (unlikely(1 & (unsigned long)from)) {
		movs("b", to, from);
		n--;
	}
	if (n > 1 && unlikely(2 & (unsigned long)from)) {
		movs("w", to, from);
		n-=2;
	}
	rep_movs(to, (const void *)from, n);
	/* KMSAN must treat values read from devices as initialized. */
	kmsan_unpoison_memory(orig_to, orig_n);
}

static void string_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
{
	if (unlikely(!n))
		return;

	/* Make sure uninitialized memory isn't copied to devices. */
	kmsan_check_memory(from, n);
	/* Align any unaligned destination IO */
	if (unlikely(1 & (unsigned long)to)) {
		movs("b", to, from);
		n--;
	}
	if (n > 1 && unlikely(2 & (unsigned long)to)) {
		movs("w", to, from);
		n-=2;
	}
	rep_movs((void *)to, (const void *) from, n);
}

static void unrolled_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
{
	const volatile char __iomem *in = from;
	char *out = to;
	int i;

	for (i = 0; i < n; ++i)
		out[i] = readb(&in[i]);
}

static void unrolled_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
{
	volatile char __iomem *out = to;
	const char *in = from;
	int i;

	for (i = 0; i < n; ++i)
		writeb(in[i], &out[i]);
}

static void unrolled_memset_io(volatile void __iomem *a, int b, size_t c)
{
	volatile char __iomem *mem = a;
	int i;

	for (i = 0; i < c; ++i)
		writeb(b, &mem[i]);
}

void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
{
	if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
		unrolled_memcpy_fromio(to, from, n);
	else
		string_memcpy_fromio(to, from, n);
}
EXPORT_SYMBOL(memcpy_fromio);

void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
{
	if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
		unrolled_memcpy_toio(to, from, n);
	else
		string_memcpy_toio(to, from, n);
}
EXPORT_SYMBOL(memcpy_toio);

void memset_io(volatile void __iomem *a, int b, size_t c)
{
	if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) {
		unrolled_memset_io(a, b, c);
	} else {
		/*
		 * TODO: memset can mangle the IO patterns quite a bit.
		 * perhaps it would be better to use a dumb one:
		 */
		memset((void *)a, b, c);
	}
}
EXPORT_SYMBOL(memset_io);