From: Andy Lutomirski luto@kernel.org
This patch has been added to the 4.1 stable tree. If you have any objections, please let us know.
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[ Upstream commit 924c6b900cfdf376b07bccfd80e62b21914f8a5a ]
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/f1e7d965998018450a7a70c2823873686a8b21c0.150752474... Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- arch/x86/kernel/reboot.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c index 0549ae3cb332..d9ea27ec9dbd 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -93,6 +93,10 @@ 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 */