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Revision 595d153dd1022392083ac93a1550382cbee127e0 authored by Michael Ellerman on 26 May 2020, 06:18:08 UTC, committed by Michael Ellerman on 26 May 2020, 07:32:37 UTC 
powerpc/64s: Fix restore of NV GPRs after facility unavailable exception
 
Commit 702f09805222 ("powerpc/64s/exception: Remove lite interrupt
return") changed the interrupt return path to not restore non-volatile
registers by default, and explicitly restore them in paths where it is
required.

But it missed that the facility unavailable exception can sometimes
modify user registers, ie. when it does emulation of move from DSCR.

This is seen as a failure of the dscr_sysfs_thread_test:
  test: dscr_sysfs_thread_test
  [cpu 0] User DSCR should be 1 but is 0
  failure: dscr_sysfs_thread_test

So restore non-volatile GPRs after facility unavailable exceptions.

Currently the hypervisor facility unavailable exception is also wired
up to call facility_unavailable_exception().

In practice we should never take a hypervisor facility unavailable
exception for the DSCR. On older bare metal systems we set HFSCR_DSCR
unconditionally in __init_HFSCR, or on newer systems it should be
enabled via the "data-stream-control-register" device tree CPU
feature.

Even if it's not, since commit f3c99f97a3cd ("KVM: PPC: Book3S HV:
Don't access HFSCR, LPIDR or LPCR when running nested"), the KVM code
has unconditionally set HFSCR_DSCR when running guests.

So we should only get a hypervisor facility unavailable for the DSCR
if skiboot has disabled the "data-stream-control-register" feature,
and we are somehow in guest context but not via KVM.

Given all that, it should be unnecessary to add a restore of
non-volatile GPRs after the hypervisor facility exception, because we
never expect to hit that path. But equally we may as well add the
restore, because we never expect to hit that path, and if we ever did,
at least we would correctly restore the registers to their post
emulation state.

In future we can split the non-HV and HV facility unavailable handling
so that there is no emulation in the HV handler, and then remove the
restore for the HV case.

Fixes: 702f09805222 ("powerpc/64s/exception: Remove lite interrupt return")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200526061808.2472279-1-mpe@ellerman.id.au
1 parent 8659a0e
Raw File
util.c 
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2002-2005 Roman Zippel <zippel@linux-m68k.org>
 * Copyright (C) 2002-2005 Sam Ravnborg <sam@ravnborg.org>
 */

#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#include "lkc.h"

/* file already present in list? If not add it */
struct file *file_lookup(const char *name)
{
	struct file *file;

	for (file = file_list; file; file = file->next) {
		if (!strcmp(name, file->name)) {
			return file;
		}
	}

	file = xmalloc(sizeof(*file));
	memset(file, 0, sizeof(*file));
	file->name = xstrdup(name);
	file->next = file_list;
	file_list = file;
	return file;
}

/* Allocate initial growable string */
struct gstr str_new(void)
{
	struct gstr gs;
	gs.s = xmalloc(sizeof(char) * 64);
	gs.len = 64;
	gs.max_width = 0;
	strcpy(gs.s, "\0");
	return gs;
}

/* Free storage for growable string */
void str_free(struct gstr *gs)
{
	if (gs->s)
		free(gs->s);
	gs->s = NULL;
	gs->len = 0;
}

/* Append to growable string */
void str_append(struct gstr *gs, const char *s)
{
	size_t l;
	if (s) {
		l = strlen(gs->s) + strlen(s) + 1;
		if (l > gs->len) {
			gs->s = xrealloc(gs->s, l);
			gs->len = l;
		}
		strcat(gs->s, s);
	}
}

/* Append printf formatted string to growable string */
void str_printf(struct gstr *gs, const char *fmt, ...)
{
	va_list ap;
	char s[10000]; /* big enough... */
	va_start(ap, fmt);
	vsnprintf(s, sizeof(s), fmt, ap);
	str_append(gs, s);
	va_end(ap);
}

/* Retrieve value of growable string */
const char *str_get(struct gstr *gs)
{
	return gs->s;
}

void *xmalloc(size_t size)
{
	void *p = malloc(size);
	if (p)
		return p;
	fprintf(stderr, "Out of memory.\n");
	exit(1);
}

void *xcalloc(size_t nmemb, size_t size)
{
	void *p = calloc(nmemb, size);
	if (p)
		return p;
	fprintf(stderr, "Out of memory.\n");
	exit(1);
}

void *xrealloc(void *p, size_t size)
{
	p = realloc(p, size);
	if (p)
		return p;
	fprintf(stderr, "Out of memory.\n");
	exit(1);
}

char *xstrdup(const char *s)
{
	char *p;

	p = strdup(s);
	if (p)
		return p;
	fprintf(stderr, "Out of memory.\n");
	exit(1);
}

char *xstrndup(const char *s, size_t n)
{
	char *p;

	p = strndup(s, n);
	if (p)
		return p;
	fprintf(stderr, "Out of memory.\n");
	exit(1);
}
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