arch/x86/kernel/cpu/mtrr/amd.c

Source file repositories/reference/linux-study-clean/arch/x86/kernel/cpu/mtrr/amd.c

File Facts

System
Linux kernel
Corpus path
arch/x86/kernel/cpu/mtrr/amd.c
Extension
.c
Size
3088 bytes
Lines
120
Domain
Architecture Layer
Bucket
arch/x86
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/mm.h>
#include <asm/mtrr.h>
#include <asm/msr.h>

#include "mtrr.h"

static void
amd_get_mtrr(unsigned int reg, unsigned long *base,
	     unsigned long *size, mtrr_type *type)
{
	unsigned long low, high;

	rdmsr(MSR_K6_UWCCR, low, high);
	/* Upper dword is region 1, lower is region 0 */
	if (reg == 1)
		low = high;
	/* The base masks off on the right alignment */
	*base = (low & 0xFFFE0000) >> PAGE_SHIFT;
	*type = 0;
	if (low & 1)
		*type = MTRR_TYPE_UNCACHABLE;
	if (low & 2)
		*type = MTRR_TYPE_WRCOMB;
	if (!(low & 3)) {
		*size = 0;
		return;
	}
	/*
	 * This needs a little explaining. The size is stored as an
	 * inverted mask of bits of 128K granularity 15 bits long offset
	 * 2 bits.
	 *
	 * So to get a size we do invert the mask and add 1 to the lowest
	 * mask bit (4 as its 2 bits in). This gives us a size we then shift
	 * to turn into 128K blocks.
	 *
	 * eg              111 1111 1111 1100      is 512K
	 *
	 * invert          000 0000 0000 0011
	 * +1              000 0000 0000 0100
	 * *128K   ...
	 */
	low = (~low) & 0x1FFFC;
	*size = (low + 4) << (15 - PAGE_SHIFT);
}

/**
 * amd_set_mtrr - Set variable MTRR register on the local CPU.
 *
 * @reg The register to set.
 * @base The base address of the region.
 * @size The size of the region. If this is 0 the region is disabled.
 * @type The type of the region.
 *
 * Returns nothing.
 */
static void
amd_set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type type)
{
	u32 regs[2];

	/*
	 * Low is MTRR0, High MTRR 1
	 */
	rdmsr(MSR_K6_UWCCR, regs[0], regs[1]);
	/*
	 * Blank to disable
	 */
	if (size == 0) {
		regs[reg] = 0;
	} else {
		/*
		 * Set the register to the base, the type (off by one) and an
		 * inverted bitmask of the size The size is the only odd
		 * bit. We are fed say 512K We invert this and we get 111 1111
		 * 1111 1011 but if you subtract one and invert you get the
		 * desired 111 1111 1111 1100 mask
		 *
		 *  But ~(x - 1) == ~x + 1 == -x. Two's complement rocks!
		 */
		regs[reg] = (-size >> (15 - PAGE_SHIFT) & 0x0001FFFC)
		    | (base << PAGE_SHIFT) | (type + 1);
	}

	/*
	 * The writeback rule is quite specific. See the manual. Its
	 * disable local interrupts, write back the cache, set the mtrr
	 */

Annotation

Implementation Notes