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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
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@ -105,6 +105,10 @@ void __noreturn machine_real_restart(unsigned int type)
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load_cr3(initial_page_table);
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#else
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write_cr3(real_mode_header->trampoline_pgd);
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/* Exiting long mode will fail if CR4.PCIDE is set. */
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if (static_cpu_has(X86_FEATURE_PCID))
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cr4_clear_bits(X86_CR4_PCIDE);
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#endif
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/* Jump to the identity-mapped low memory code */
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