linux-kernel - [tip:efi/urgent] x86/mm: Fix bogus warning during EFI bootup, use boot_cpu_has() instead of this_cpu_has() in build_cr3

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Date:   Wed, 4 Apr 2018 16:31:28 -0700
From:   tip-bot for Sai Praneeth <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     jlee@...e.com, ravi.v.shankar@...el.com, matt@...eblueprint.co.uk,
        a.p.zijlstra@...llo.nl, luto@...nel.org, akpm@...ux-foundation.org,
        tony.luck@...el.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        dave.hansen@...el.com, mst@...hat.com, ricardo.neri@...el.com,
        sai.praneeth.prakhya@...el.com, hpa@...or.com,
        ard.biesheuvel@...aro.org, peterz@...radead.org,
        tglx@...utronix.de, bp@...en8.de
Subject: [tip:efi/urgent] x86/mm: Fix bogus warning during EFI bootup, use
 boot_cpu_has() instead of this_cpu_has() in build_cr3_noflush()

Commit-ID:  162ee5a8ab49be40d253f90e94aef712470a3a24
Gitweb:     https://git.kernel.org/tip/162ee5a8ab49be40d253f90e94aef712470a3a24
Author:     Sai Praneeth <sai.praneeth.prakhya@...el.com>
AuthorDate: Wed, 4 Apr 2018 12:34:19 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 5 Apr 2018 01:27:49 +0200

x86/mm: Fix bogus warning during EFI bootup, use boot_cpu_has() instead of this_cpu_has() in build_cr3_noflush()

Linus reported the following boot warning:

  WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/tlbflush.h:134 load_new_mm_cr3+0x114/0x170
  [...]
  Call Trace:
  switch_mm_irqs_off+0x267/0x590
  switch_mm+0xe/0x20
  efi_switch_mm+0x3e/0x50
  efi_enter_virtual_mode+0x43f/0x4da
  start_kernel+0x3bf/0x458
  secondary_startup_64+0xa5/0xb0

... after merging:

  03781e40890c: x86/efi: Use efi_switch_mm() rather than manually twiddling with %cr3

When the platform supports PCID and if CONFIG_DEBUG_VM=y is enabled,
build_cr3_noflush() (called via switch_mm()) does a sanity check to see
if X86_FEATURE_PCID is set.

Presently, build_cr3_noflush() uses "this_cpu_has(X86_FEATURE_PCID)" to
perform the check but this_cpu_has() works only after SMP is initialized
(i.e. per cpu cpu_info's should be populated) and this happens to be very
late in the boot process (during rest_init()).

As efi_runtime_services() are called during (early) kernel boot time
and run time, modify build_cr3_noflush() to use boot_cpu_has() all the
time. As suggested by Dave Hansen, this should be OK because all CPU's have
same capabilities on x86.

With this change the warning is fixed.

( Dave also suggested that we put a warning in this_cpu_has() if it's used
  early in the boot process. This is still work in progress as it affects
  MCE. )

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Lee Chun-Yi <jlee@...e.com>
Cc: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ravi Shankar <ravi.v.shankar@...el.com>
Cc: Ricardo Neri <ricardo.neri@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tony Luck <tony.luck@...el.com>
Cc: linux-efi@...r.kernel.org
Link: http://lkml.kernel.org/r/1522870459-7432-1-git-send-email-sai.praneeth.prakhya@intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/tlbflush.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 84137c22fdfa..6690cd3fc8b1 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -131,7 +131,12 @@ static inline unsigned long build_cr3(pgd_t *pgd, u16 asid)
 static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
 {
 	VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
-	VM_WARN_ON_ONCE(!this_cpu_has(X86_FEATURE_PCID));
+	/*
+	 * Use boot_cpu_has() instead of this_cpu_has() as this function
+	 * might be called during early boot. This should work even after
+	 * boot because all CPU's the have same capabilities:
+	 */
+	VM_WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_PCID));
 	return __sme_pa(pgd) | kern_pcid(asid) | CR3_NOFLUSH;
 }