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SubjectRe: [PATCH 00/15] KVM: x86: fully implement vMTRR


On 05/30/2015 06:59 PM, Xiao Guangrong wrote:
> Currently guest MTRR is completely prohibited if cache snoop is supported on
> IOMMU (!noncoherent_dma) and host does the emulation based on the knowledge
> from host side, however, host side is not the good point to know
> what the purpose of guest is. A good example is that pass-throughed VGA
> frame buffer is not always UC as host expected
>
> Besides that, there is a bugs in current code if noncoherent_dma is detected:
> KVM still uses hugepage even if the 4K pages in that ranges span between
> on different memory types and uses the cache type of first page to do memory
> mapping
>
> This patchset enables full MTRR virtualization and currently only works on
> Intel EPT architecture
>
> There is the code will be attached in this thread is used to check the effect
> of this patchset:
> [12834.843439] __INIT__.
> [12835.909109] Running in preload MTRR_TYPE_UNCACHABLE 4753900 ns.
> [12835.915232] Running in MTRR_TYPE_UNCACHABLE 5257522 ns.
> [12838.083948] Running in preload MTRR_TYPE_WRBACK 13266 ns.
> [12838.084998] Running in MTRR_TYPE_WRBACK 13099 ns.
>

Has been attached in this mail.
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/delay.h>
#include <linux/fb.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/init.h>
#include <linux/pci.h>
#include <asm/io.h>
#include <linux/uaccess.h>

#ifdef CONFIG_MTRR
#include <asm/mtrr.h>
#endif

//#define DEBUG

#ifdef DEBUG
#define dprintk(fmt, args...) \
printk(fmt, ##args)
#define debug_show_mtrr() show_mtrr()
#else
//#define pr_debug(format, ...) do {} while (0)
#define dprintk(fmt, ...) do {} while (0)
#define debug_show_mtrr() do {} while (0)
#endif

MODULE_LICENSE("GPL");

#define NR_PAGES_ORDER 1

static u64 __do_write(struct page *page, int page_nr)
{
void *addr = page_address(page);
u64 total = 0;
int i;

for (i = 0; i < PAGE_SIZE * page_nr; i++) {
((char *)addr)[i] = (char)0x99;
}

return total;
}

static u64 __do_read(struct page *page, int page_nr)
{
void *addr = page_address(page);
u64 total = 0;
int i;

for (i = 0; i < PAGE_SIZE * page_nr; i++) {
total += ((char *)addr)[i];
if (((char *)addr)[i] != (char)0x99) {
printk("read failed %x expected 0x99.\n", ((char *)addr)[i]);
break;
}
}

return total;
}

static void do_rw(struct page *page, int page_nr, const char *cachetype)
{
ktime_t start, end;
u64 total;

start = ktime_get();
__do_write(page, page_nr);
total = __do_read(page, page_nr);
end = ktime_get();
printk("Running in %s %lld ns.\n", cachetype,
ktime_to_ns(ktime_sub(end, start)));
}

static int add_region_to_mtrr(struct page *page, int page_nr, int type,
const char *cachetype)
{
unsigned long pfn;
int ret;

pfn = page_to_pfn(page);

ret = mtrr_add(pfn << PAGE_SHIFT, PAGE_SIZE * page_nr, type, 1);
if (ret < 0)
printk("mtrr_add %s failed, return %d.\n", cachetype, ret);

dprintk("%s add region %lx nrpage %d.\n", cachetype, pfn << PAGE_SHIFT, page_nr);
return ret;
}

static int del_region_from_mtrr(int entry, struct page *page, int page_nr, const char *cachetype)
{
unsigned long pfn;
int ret;

pfn = page_to_pfn(page);

ret = mtrr_del(entry, pfn << PAGE_SHIFT, PAGE_SIZE * page_nr);
if (ret < 0)
printk("mtrr_del %s failed, return %d.\n", cachetype, ret);
dprintk("%s del region %lx nrpage %d.\n", cachetype, pfn << PAGE_SHIFT, page_nr);
return ret;
}

static int memory_rw(void)
{
struct page *page;
int page_order, page_nr, ret;

page_order = NR_PAGES_ORDER;
page_nr = 1 << page_order;

page = alloc_pages(GFP_KERNEL, page_order);
if (!page)
return -ENOMEM;

ret = add_region_to_mtrr(page, page_nr, MTRR_TYPE_UNCACHABLE,
"MTRR_TYPE_UNCACHABLE");
if (ret < 0)
goto exit;

do_rw(page, page_nr, "preload MTRR_TYPE_UNCACHABLE");
do_rw(page, page_nr, "MTRR_TYPE_UNCACHABLE");

ret = del_region_from_mtrr(ret, page, page_nr, "MTRR_TYPE_UNCACHABLE");
if (ret < 0)
goto exit;

ret = add_region_to_mtrr(page, page_nr, MTRR_TYPE_WRBACK,
"MTRR_TYPE_WRBACK");
if (ret < 0)
goto exit;

do_rw(page, page_nr, "preload MTRR_TYPE_WRBACK");
do_rw(page, page_nr, "MTRR_TYPE_WRBACK");

ret = del_region_from_mtrr(ret, page, page_nr, "MTRR_TYPE_WRBACK");
if (ret < 0)
goto exit;

ret = 0;
exit:
__free_pages(page, page_order);
return ret;

}

static int __init my_init(void)
{
printk("__INIT__.\n");

dprintk("######### INIT MTRR...\n");

return memory_rw();
}

static void __exit my_exit(void)
{
dprintk("###### EXIT MTRR...\n");
return;
}

module_init(my_init)
module_exit(my_exit)

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