arm64 regression in kernel 5.12 related to the (n)VHE

[Rafał Miłecki]

On 12.08.2021 08:51, Marc Zyngier wrote:
> Interestingly, all your CPUs are booting at EL2. Which is great.  Can
> you try and enable KVM on your existing 5.10 kernel? Just selecting
> CONFIG_KVM should be enough. Does it boot correctly with KVM enabled?
> 
> My suspicion is that the firmware doesn't set SCR_EL3.HCE, and that
> the HVC instruction UNDEFs at EL1. That would be bad news.

Interesting! I had to enable CONFIG_VIRTUALIZATION and CONFIG_NET first.
First I verified kernel built with those options still boots. It does.

Then I enabled CONFIG_KVM and kernel seems to hang around switching from
bootconsole to the console.

Starting program at 0x0000000000080000
/memory = 0x40000000
WARNING: Node's property /reserved-memory/dt_reserved_buffer is not defined
WARNING: Node's property /reserved-memory/dt_reserved_flow is not defined
WARNING: Node's property /reserved-memory/dt_reserved_dhd2 is not defined
Booting Linux on physical CPU 0x0000000000 [0x420f1000]
Linux version 5.11.22-g0453a426c37b (rmilecki at localhost.localdomain) (aarch64-buildroot-linux-uclibc-gcc.br_real (Buildroot -g91617ed) 9.3.0, GNU ld (GNU Binutils) 2.33.1) #8 SMP Thu Aug 12 09:25:55 CEST 2021
Machine model: Asus GT-AC5300
earlycon: bcm63xx_uart0 at MMIO 0x00000000ff800640 (options '')
printk: bootconsole [bcm63xx_uart0] enabled
efi: UEFI not found.
[Firmware Bug]: Kernel image misaligned at boot, please fix your bootloader!
Zone ranges:
   DMA      [mem 0x0000000000000000-0x000000003fffffff]
   DMA32    empty
   Normal   empty
Movable zone start for each node
Early memory node ranges
   node   0: [mem 0x0000000000000000-0x000000003fffffff]
Initmem setup node 0 [mem 0x0000000000000000-0x000000003fffffff]
percpu: Embedded 18 pages/cpu s43904 r0 d29824 u73728
Detected VIPT I-cache on CPU0
CPU features: detected: ARM erratum 843419
Built 1 zonelists, mobility grouping on.  Total pages: 258048
Kernel command line: earlycon=bcm63xx_uart,0xff800640
Dentry cache hash table entries: 131072 (order: 8, 1048576 bytes, linear)
Inode-cache hash table entries: 65536 (order: 7, 524288 bytes, linear)
mem auto-init: stack:off, heap alloc:off, heap free:off
Memory: 1019556K/1048576K available (4352K kernel code, 678K rwdata, 860K rodata, 2496K init, 232K bss, 29020K reserved, 0K cma-reserved)
SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
rcu: Hierarchical RCU implementation.
rcu: RCU calculated value of scheduler-enlistment delay is 25 jiffies.
NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0
GIC: Using split EOI/Deactivate mode
random: get_random_bytes called from start_kernel+0x33c/0x52c with crng_init=0
arch_timer: cp15 timer(s) running at 50.00MHz (phys).
clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycles: 0xb8812736b, max_idle_ns: 440795202655 ns
sched_clock: 56 bits at 50MHz, resolution 20ns, wraps every 4398046511100ns
Console: colour dummy device 80x25
printk: console [tty0] enabled
printk: bootconsole [bcm63xx_uart0] disabled


(Unless it's a false conclusion and CONFIG_KVM just breaks console
somehow)


Enabling CONFIG_KVM resulted in enablig few more options but I believe
it's actually CONFIG_KVM itself that affects booting process.

--- config-nokvm        2021-08-12 09:21:50.670046231 +0200
+++ config-kvm  2021-08-12 09:22:35.897103038 +0200
@@ -292,6 +292,7 @@
  CONFIG_ARM64_ERRATUM_824069=y
  CONFIG_ARM64_ERRATUM_819472=y
  CONFIG_ARM64_ERRATUM_832075=y
+CONFIG_ARM64_ERRATUM_834220=y
  CONFIG_ARM64_ERRATUM_843419=y
  CONFIG_ARM64_ERRATUM_1024718=y
  CONFIG_ARM64_WORKAROUND_SPECULATIVE_AT=y
@@ -502,8 +503,21 @@

  CONFIG_ARCH_SUPPORTS_ACPI=y
  # CONFIG_ACPI is not set
+CONFIG_IRQ_BYPASS_MANAGER=y
  CONFIG_VIRTUALIZATION=y
-# CONFIG_KVM is not set
+CONFIG_KVM=y
+CONFIG_HAVE_KVM_IRQCHIP=y
+CONFIG_HAVE_KVM_IRQFD=y
+CONFIG_HAVE_KVM_IRQ_ROUTING=y
+CONFIG_HAVE_KVM_EVENTFD=y
+CONFIG_KVM_MMIO=y
+CONFIG_HAVE_KVM_MSI=y
+CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT=y
+CONFIG_KVM_VFIO=y
+CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL=y
+CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT=y
+CONFIG_HAVE_KVM_IRQ_BYPASS=y
+CONFIG_HAVE_KVM_VCPU_RUN_PID_CHANGE=y

  #
  # General architecture-dependent options
@@ -616,6 +630,7 @@
  # CONFIG_IOSCHED_BFQ is not set
  # end of IO Schedulers

+CONFIG_PREEMPT_NOTIFIERS=y
  CONFIG_ARCH_INLINE_SPIN_TRYLOCK=y
  CONFIG_ARCH_INLINE_SPIN_TRYLOCK_BH=y
  CONFIG_ARCH_INLINE_SPIN_LOCK=y
@@ -712,6 +727,7 @@
  CONFIG_MIGRATION=y
  CONFIG_PHYS_ADDR_T_64BIT=y
  CONFIG_BOUNCE=y
+CONFIG_MMU_NOTIFIER=y
  # CONFIG_KSM is not set
  CONFIG_DEFAULT_MMAP_MIN_ADDR=4096
  CONFIG_ARCH_SUPPORTS_MEMORY_FAILURE=y
@@ -2508,6 +2524,7 @@
  CONFIG_DECOMPRESS_LZ4=y
  CONFIG_DECOMPRESS_ZSTD=y
  CONFIG_GENERIC_ALLOCATOR=y
+CONFIG_INTERVAL_TREE=y
  CONFIG_HAS_IOMEM=y
  CONFIG_HAS_IOPORT_MAP=y
  CONFIG_HAS_DMA=y