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
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
kheaders.c
// SPDX-License-Identifier: GPL-2.0
/*
* Provide kernel headers useful to build tracing programs
* such as for running eBPF tracing tools.
*
* (Borrowed code from kernel/configs.c)
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/init.h>
/*
* Define kernel_headers_data and kernel_headers_data_end, within which the
* compressed kernel headers are stored. The file is first compressed with xz.
*/
asm (
" .pushsection .rodata, \"a\" \n"
" .global kernel_headers_data \n"
"kernel_headers_data: \n"
" .incbin \"kernel/kheaders_data.tar.xz\" \n"
" .global kernel_headers_data_end \n"
"kernel_headers_data_end: \n"
" .popsection \n"
);
extern char kernel_headers_data;
extern char kernel_headers_data_end;
static ssize_t
ikheaders_read(struct file *file, struct kobject *kobj,
struct bin_attribute *bin_attr,
char *buf, loff_t off, size_t len)
{
memcpy(buf, &kernel_headers_data + off, len);
return len;
}
static struct bin_attribute kheaders_attr __ro_after_init = {
.attr = {
.name = "kheaders.tar.xz",
.mode = 0444,
},
.read = &ikheaders_read,
};
static int __init ikheaders_init(void)
{
kheaders_attr.size = (&kernel_headers_data_end -
&kernel_headers_data);
return sysfs_create_bin_file(kernel_kobj, &kheaders_attr);
}
static void __exit ikheaders_cleanup(void)
{
sysfs_remove_bin_file(kernel_kobj, &kheaders_attr);
}
module_init(ikheaders_init);
module_exit(ikheaders_cleanup);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Joel Fernandes");
MODULE_DESCRIPTION("Echo the kernel header artifacts used to build the kernel");
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