From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andy Lutomirski , Thomas Gleixner , Borislav Petkov , Hugh Dickins Subject: [PATCH 4.9 22/75] x86/mm/64: Fix reboot interaction with CR4.PCIDE Date: Mon, 1 Jan 2018 15:31:59 +0100 Message-Id: <20180101140100.064836110@linuxfoundation.org> In-Reply-To: <20180101140056.475827799@linuxfoundation.org> References: <20180101140056.475827799@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andy Lutomirski 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) Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Cc: Borislav Petkov Link: https://lkml.kernel.org/r/f1e7d965998018450a7a70c2823873686a8b21c0.1507524746.git.luto@kernel.org Cc: Hugh Dickins Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/reboot.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -106,6 +106,10 @@ void __noreturn machine_real_restart(uns 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 */