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, 7 insertions, 42 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index fb1d3358a4af..775f10100d7f 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -169,21 +169,21 @@ static int __init x86_mpx_setup(char *s)
 __setup("nompx", x86_mpx_setup);
 
 #ifdef CONFIG_X86_64
-static int __init x86_pcid_setup(char *s)
+static int __init x86_nopcid_setup(char *s)
 {
-	/* require an exact match without trailing characters */
-	if (strlen(s))
-		return 0;
+	/* nopcid doesn't accept parameters */
+	if (s)
+		return -EINVAL;
 
 	/* do not emit a message if the feature is not present */
 	if (!boot_cpu_has(X86_FEATURE_PCID))
-		return 1;
+		return 0;
 
 	setup_clear_cpu_cap(X86_FEATURE_PCID);
 	pr_info("nopcid: PCID feature disabled\n");
-	return 1;
+	return 0;
 }
-__setup("nopcid", x86_pcid_setup);
+early_param("nopcid", x86_nopcid_setup);
 #endif
 
 static int __init x86_noinvpcid_setup(char *s)
@@ -329,38 +329,6 @@ static __always_inline void setup_smap(struct cpuinfo_x86 *c)
 	}
 }
 
-static void setup_pcid(struct cpuinfo_x86 *c)
-{
-	if (cpu_has(c, X86_FEATURE_PCID)) {
-		if (cpu_has(c, X86_FEATURE_PGE)) {
-			/*
-			 * We'd like to use cr4_set_bits_and_update_boot(),
-			 * but we can't.  CR4.PCIDE is special and can only
-			 * be set in long mode, and the early CPU init code
-			 * doesn't know this and would try to restore CR4.PCIDE
-			 * prior to entering long mode.
-			 *
-			 * Instead, we rely on the fact that hotplug, resume,
-			 * etc all fully restore CR4 before they write anything
-			 * that could have nonzero PCID bits to CR3.  CR4.PCIDE
-			 * has no effect on the page tables themselves, so we
-			 * don't need it to be restored early.
-			 */
-			cr4_set_bits(X86_CR4_PCIDE);
-		} else {
-			/*
-			 * flush_tlb_all(), as currently implemented, won't
-			 * work if PCID is on but PGE is not.  Since that
-			 * combination doesn't exist on real hardware, there's
-			 * no reason to try to fully support it, but it's
-			 * polite to avoid corrupting data if we're on
-			 * an improperly configured VM.
-			 */
-			clear_cpu_cap(c, X86_FEATURE_PCID);
-		}
-	}
-}
-
 /*
  * Protection Keys are not available in 32-bit mode.
  */
@@ -1175,9 +1143,6 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 	setup_smep(c);
 	setup_smap(c);
 
-	/* Set up PCID */
-	setup_pcid(c);
-
 	/*
 	 * The vendor-specific functions might have changed features.
 	 * Now we do "generic changes."