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authorAndy Lutomirski <luto@kernel.org>2017-10-08 21:53:05 -0700
committerThomas Gleixner <tglx@linutronix.de>2017-10-09 13:31:04 +0200
commit924c6b900cfdf376b07bccfd80e62b21914f8a5a (patch)
tree9b85f57af2c7b646e284b194636d925c6e265e7a
parentb664d57f39d01e775204d4f1a7e2f8bda77bc549 (diff)
x86/mm/64: Fix reboot interaction with CR4.PCIDE
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
-rw-r--r--arch/x86/kernel/reboot.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 54180fa6f66f..add33f600531 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -105,6 +105,10 @@ void __noreturn machine_real_restart(unsigned int type)
load_cr3(initial_page_table);
#else
write_cr3(real_mode_header->trampoline_pgd);
+
+ /* Exiting long mode will fail if CR4.PCIDE is set. */
+ if (static_cpu_has(X86_FEATURE_PCID))
+ cr4_clear_bits(X86_CR4_PCIDE);
#endif
/* Jump to the identity-mapped low memory code */