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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
configs.c 
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * kernel/configs.c
 * Echo the kernel .config file used to build the kernel
 *
 * Copyright (C) 2002 Khalid Aziz <khalid_aziz@hp.com>
 * Copyright (C) 2002 Randy Dunlap <rdunlap@xenotime.net>
 * Copyright (C) 2002 Al Stone <ahs3@fc.hp.com>
 * Copyright (C) 2002 Hewlett-Packard Company
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/init.h>
#include <linux/uaccess.h>

/*
 * "IKCFG_ST" and "IKCFG_ED" are used to extract the config data from
 * a binary kernel image or a module. See scripts/extract-ikconfig.
 */
asm (
"	.pushsection .rodata, \"a\"		\n"
"	.ascii \"IKCFG_ST\"			\n"
"	.global kernel_config_data		\n"
"kernel_config_data:				\n"
"	.incbin \"kernel/config_data.gz\"	\n"
"	.global kernel_config_data_end		\n"
"kernel_config_data_end:			\n"
"	.ascii \"IKCFG_ED\"			\n"
"	.popsection				\n"
);

#ifdef CONFIG_IKCONFIG_PROC

extern char kernel_config_data;
extern char kernel_config_data_end;

static ssize_t
ikconfig_read_current(struct file *file, char __user *buf,
		      size_t len, loff_t * offset)
{
	return simple_read_from_buffer(buf, len, offset,
				       &kernel_config_data,
				       &kernel_config_data_end -
				       &kernel_config_data);
}

static const struct proc_ops config_gz_proc_ops = {
	.proc_read	= ikconfig_read_current,
	.proc_lseek	= default_llseek,
};

static int __init ikconfig_init(void)
{
	struct proc_dir_entry *entry;

	/* create the current config file */
	entry = proc_create("config.gz", S_IFREG | S_IRUGO, NULL,
			    &config_gz_proc_ops);
	if (!entry)
		return -ENOMEM;

	proc_set_size(entry, &kernel_config_data_end - &kernel_config_data);

	return 0;
}

static void __exit ikconfig_cleanup(void)
{
	remove_proc_entry("config.gz", NULL);
}

module_init(ikconfig_init);
module_exit(ikconfig_cleanup);

#endif /* CONFIG_IKCONFIG_PROC */

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Randy Dunlap");
MODULE_DESCRIPTION("Echo the kernel .config file used to build the kernel");
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