x86/mm/64: Initialize CR4.PCIDE early

cpu_init() is weird: it's called rather late (after early
identification and after most MMU state is initialized) on the boot
CPU but is called extremely early (before identification) on secondary
CPUs.  It's called just late enough on the boot CPU that its CR4 value
isn't propagated to mmu_cr4_features.

Even if we put CR4.PCIDE into mmu_cr4_features, we'd hit two
problems.  First, we'd crash in the trampoline code.  That's
fixable, and I tried that.  It turns out that mmu_cr4_features is
totally ignored by secondary_start_64(), though, so even with the
trampoline code fixed, it wouldn't help.

This means that we don't currently have CR4.PCIDE reliably initialized
before we start playing with cpu_tlbstate.  This is very fragile and
tends to cause boot failures if I make even small changes to the TLB
handling code.

Make it more robust: initialize CR4.PCIDE earlier on the boot CPU
and propagate it to secondary CPUs in start_secondary().

( Yes, this is ugly.  I think we should have improved mmu_cr4_features
  to actually control CR4 during secondary bootup, but that would be
  fairly intrusive at this stage. )

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reported-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Tested-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Fixes: 660da7c9228f ("x86/mm: Enable CR4.PCIDE on supported systems")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index cd6622c3204e..0854ff169274 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -226,10 +226,12 @@ static int enable_start_cpu0;
 static void notrace start_secondary(void *unused)
 {
 	/*
-	 * Don't put *anything* before cpu_init(), SMP booting is too
-	 * fragile that we want to limit the things done here to the
-	 * most necessary things.
+	 * Don't put *anything* except direct CPU state initialization
+	 * before cpu_init(), SMP booting is too fragile that we want to
+	 * limit the things done here to the most necessary things.
 	 */
+	if (boot_cpu_has(X86_FEATURE_PCID))
+		__write_cr4(__read_cr4() | X86_CR4_PCIDE);
 	cpu_init();
 	x86_cpuinit.early_percpu_clock_init();
 	preempt_disable();