Skip to main content

Browse the archive

https://github.com/torvalds/linux
05 April 2024, 19:05:47 UTC
Revision 23316316c1af0677a041c81f3ad6efb9dc470b33 authored by Paul Mackerras on 21 October 2015, 05:03:14 UTC, committed by Michael Ellerman on 21 October 2015, 09:50:30 UTC 
powerpc: Revert "Use the POWER8 Micro Partition Prefetch Engine in KVM HV on POWER8"
 
This reverts commit 9678cdaae939 ("Use the POWER8 Micro Partition
Prefetch Engine in KVM HV on POWER8") because the original commit had
multiple, partly self-cancelling bugs, that could cause occasional
memory corruption.

In fact the logmpp instruction was incorrectly using register r0 as the
source of the buffer address and operation code, and depending on what
was in r0, it would either do nothing or corrupt the 64k page pointed to
by r0.

The logmpp instruction encoding and the operation code definitions could
be corrected, but then there is the problem that there is no clearly
defined way to know when the hardware has finished writing to the
buffer.

The original commit attempted to work around this by aborting the
write-out before starting the prefetch, but this is ineffective in the
case where the virtual core is now executing on a different physical
core from the one where the write-out was initiated.

These problems plus advice from the hardware designers not to use the
function (since the measured performance improvement from using the
feature was actually mostly negative), mean that reverting the code is
the best option.

Fixes: 9678cdaae939 ("Use the POWER8 Micro Partition Prefetch Engine in KVM HV on POWER8")
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
1 parent abb39bc
Raw File
Tip revision: 23316316c1af0677a041c81f3ad6efb9dc470b33 authored by Paul Mackerras on 21 October 2015, 05:03:14 UTC
powerpc: Revert "Use the POWER8 Micro Partition Prefetch Engine in KVM HV on POWER8"
Tip revision: 2331631
range.c 
/*
 * Range add and subtract
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sort.h>
#include <linux/string.h>
#include <linux/range.h>

int add_range(struct range *range, int az, int nr_range, u64 start, u64 end)
{
	if (start >= end)
		return nr_range;

	/* Out of slots: */
	if (nr_range >= az)
		return nr_range;

	range[nr_range].start = start;
	range[nr_range].end = end;

	nr_range++;

	return nr_range;
}

int add_range_with_merge(struct range *range, int az, int nr_range,
		     u64 start, u64 end)
{
	int i;

	if (start >= end)
		return nr_range;

	/* get new start/end: */
	for (i = 0; i < nr_range; i++) {
		u64 common_start, common_end;

		if (!range[i].end)
			continue;

		common_start = max(range[i].start, start);
		common_end = min(range[i].end, end);
		if (common_start > common_end)
			continue;

		/* new start/end, will add it back at last */
		start = min(range[i].start, start);
		end = max(range[i].end, end);

		memmove(&range[i], &range[i + 1],
			(nr_range - (i + 1)) * sizeof(range[i]));
		range[nr_range - 1].start = 0;
		range[nr_range - 1].end   = 0;
		nr_range--;
		i--;
	}

	/* Need to add it: */
	return add_range(range, az, nr_range, start, end);
}

void subtract_range(struct range *range, int az, u64 start, u64 end)
{
	int i, j;

	if (start >= end)
		return;

	for (j = 0; j < az; j++) {
		if (!range[j].end)
			continue;

		if (start <= range[j].start && end >= range[j].end) {
			range[j].start = 0;
			range[j].end = 0;
			continue;
		}

		if (start <= range[j].start && end < range[j].end &&
		    range[j].start < end) {
			range[j].start = end;
			continue;
		}


		if (start > range[j].start && end >= range[j].end &&
		    range[j].end > start) {
			range[j].end = start;
			continue;
		}

		if (start > range[j].start && end < range[j].end) {
			/* Find the new spare: */
			for (i = 0; i < az; i++) {
				if (range[i].end == 0)
					break;
			}
			if (i < az) {
				range[i].end = range[j].end;
				range[i].start = end;
			} else {
				pr_err("%s: run out of slot in ranges\n",
					__func__);
			}
			range[j].end = start;
			continue;
		}
	}
}

static int cmp_range(const void *x1, const void *x2)
{
	const struct range *r1 = x1;
	const struct range *r2 = x2;

	if (r1->start < r2->start)
		return -1;
	if (r1->start > r2->start)
		return 1;
	return 0;
}

int clean_sort_range(struct range *range, int az)
{
	int i, j, k = az - 1, nr_range = az;

	for (i = 0; i < k; i++) {
		if (range[i].end)
			continue;
		for (j = k; j > i; j--) {
			if (range[j].end) {
				k = j;
				break;
			}
		}
		if (j == i)
			break;
		range[i].start = range[k].start;
		range[i].end   = range[k].end;
		range[k].start = 0;
		range[k].end   = 0;
		k--;
	}
	/* count it */
	for (i = 0; i < az; i++) {
		if (!range[i].end) {
			nr_range = i;
			break;
		}
	}

	/* sort them */
	sort(range, nr_range, sizeof(struct range), cmp_range, NULL);

	return nr_range;
}

void sort_range(struct range *range, int nr_range)
{
	/* sort them */
	sort(range, nr_range, sizeof(struct range), cmp_range, NULL);
}
back to top