| From: Andy Lutomirski <luto@kernel.org> |
| Date: Sun, 8 Oct 2017 21:53:05 -0700 |
| Subject: x86/mm/64: Fix reboot interaction with CR4.PCIDE |
| |
| commit 924c6b900cfdf376b07bccfd80e62b21914f8a5a upstream. |
| |
| Trying to reboot via real mode fails with PCID on: long mode cannot |
| be exited while CR4.PCIDE is set. (No, I have no idea why, but the |
| SDM and actual CPUs are in agreement here.) The result is a GPF and |
| a hang instead of a reboot. |
| |
| I didn't catch this in testing because neither my computer nor my VM |
| reboots this way. I can trigger it with reboot=bios, though. |
| |
| Fixes: 660da7c9228f ("x86/mm: Enable CR4.PCIDE on supported systems") |
| Reported-and-tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org> |
| Signed-off-by: Andy Lutomirski <luto@kernel.org> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| Cc: Borislav Petkov <bp@alien8.de> |
| Link: https://lkml.kernel.org/r/f1e7d965998018450a7a70c2823873686a8b21c0.1507524746.git.luto@kernel.org |
| Signed-off-by: Hugh Dickins <hughd@google.com> |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| arch/x86/kernel/reboot.c | 6 ++++++ |
| 1 file changed, 6 insertions(+) |
| |
| diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c |
| index a34bdddeca85..04da0bf5c314 100644 |
| --- a/arch/x86/kernel/reboot.c |
| +++ b/arch/x86/kernel/reboot.c |
| @@ -357,6 +357,12 @@ void machine_real_restart(unsigned int type) |
| lowmem_gdt[1] = |
| GDT_ENTRY(0x009b, restart_pa, 0xffff); |
| |
| +#ifdef CONFIG_X86_64 |
| + /* Exiting long mode will fail if CR4.PCIDE is set. */ |
| + if (static_cpu_has(X86_FEATURE_PCID)) |
| + clear_in_cr4(X86_CR4_PCIDE); |
| +#endif |
| + |
| /* Jump to the identity-mapped low memory code */ |
| restart_lowmem(type); |
| } |
| |
