On Mon, 9 Oct 2017 04:36:01 -0700
tip-bot for Andy Lutomirski <tipbot@xxxxxxxxx> wrote:
> Commit-ID: 924c6b900cfdf376b07bccfd80e62b21914f8a5a
> Gitweb: https://git.kernel.org/tip/924c6b900cfdf376b07bccfd80e62b21914f8a5a
> Author: Andy Lutomirski <luto@xxxxxxxxxx>
> AuthorDate: Sun, 8 Oct 2017 21:53:05 -0700
> Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CommitDate: Mon, 9 Oct 2017 13:31:04 +0200
>
> 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@xxxxxxxxxxx>
Didn't someone somewhere say not to combine tags? Have them always be
separate. I noticed they were separate when Andy submitted it, but I'm
assuming that Thomas combined it.
-- Steve
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Link: https://lkml.kernel.org/r/f1e7d965998018450a7a70c2823873686a8b21c0.1507524746.git.luto@xxxxxxxxxx
>
> ---
> 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 54180fa..add33f6 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 */
--
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