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Subject[PATCH 4.16 078/272] x86/mm: Fix bogus warning during EFI bootup, use boot_cpu_has() instead of this_cpu_has() in build_cr3_noflush()
Date
4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sai Praneeth <sai.praneeth.prakhya@intel.com>

[ Upstream commit 162ee5a8ab49be40d253f90e94aef712470a3a24 ]

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@linux-foundation.org>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Lee Chun-Yi <jlee@suse.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-efi@vger.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@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/tlbflush.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -131,7 +131,12 @@ static inline unsigned long build_cr3(pg
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;
}


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