On Fri, Dec 07, 2018 at 10:47:57AM +0000, Suzuki K Poulose wrote:

On 12/06/2018 10:50 PM, Steve Capper wrote:

quoted

For cases where there is a mismatch in ARMv8.2-LVA support between CPUs
we have to be careful in allowing secondary CPUs to boot if 52-bit
virtual addresses have already been enabled on the boot CPU.

This patch adds code to the secondary startup path. If the boot CPU has
enabled 52-bit VAs then ID_AA64MMFR2_EL1 is checked to see if the
secondary can also enable 52-bit support. If not, the secondary is
prevented from booting and an error message is displayed indicating why.

Technically this patch could be implemented using the cpufeature code
when considering 52-bit userspace support. However, we employ low level
checks here as the cpufeature code won't be able to run if we have
mismatched 52-bit kernel va support.

Signed-off-by: Steve Capper <redacted>

The patch looks good to me, except for one comment below.

quoted

---

Patch is new in V5 of the series
---
  arch/arm64/kernel/head.S | 26 ++++++++++++++++++++++++++
  arch/arm64/kernel/smp.c  |  5 +++++
  2 files changed, 31 insertions(+)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index f60081be9a1b..58fcc1edd852 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S

@@ -707,6 +707,7 @@ secondary_startup:
  	/*
  	 * Common entry point for secondary CPUs.
  	 */
+	bl	__cpu_secondary_check52bitva
  	bl	__cpu_setup			// initialise processor
  	adrp	x1, swapper_pg_dir
  	bl	__enable_mmu

@@ -785,6 +786,31 @@ ENTRY(__enable_mmu)
  	ret
  ENDPROC(__enable_mmu)
+ENTRY(__cpu_secondary_check52bitva)
+#ifdef CONFIG_ARM64_52BIT_VA
+	ldr_l	x0, vabits_user
+	cmp	x0, #52
+	b.ne	2f > +
+	mrs_s	x0, SYS_ID_AA64MMFR2_EL1
+	and	x0, x0, #(0xf << ID_AA64MMFR2_LVA_SHIFT)
+	cbnz	x0, 2f
+
+	adr_l	x0, va52mismatch
+	mov	w1, #1
+	strb	w1, [x0]
+	dmb	sy
+	dc	ivac, x0	// Invalidate potentially stale cache line

You may have to clear this variable before a CPU is brought up to avoid
raising a false error message when another secondary CPU doesn't boot
for some other reason (say granule support) after a CPU failed with lack
of 52bitva. It is really a crazy corner case.

Can't we just follow the example set by the EL2 setup in the way that is
uses __boot_cpu_mode? In that case, we only need one variable and you can
detect a problem by comparing the two halves.

Will

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel