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

[Marc Zyngier]

On Thu, 12 Aug 2021 08:32:02 +0100,
Rafał Miłecki <zajec5 at gmail.com> wrote:
> 
> 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)

No, that's because you don't pass the right console to your
kernel. Add something like "console=ttyS0,115200" to the kernel
command line, which will show what you are missing, as well as stop
the double-logging.

Anyway, the fact that it stops booting when you enable KVM confirms my
suspicion. The firmware on this system is probably crap enough not to
enable HVC. Let's confirm it further: please apply the patch below on
top of mainline and tell me that it now boots fine...

Are you in a position where you can actually fix the firmware? Or is
it some closed-source blob?

Broadcom folks: can you lease check whether the firmware on this
system correctly configures SCR_EL3.HCE?

Thanks,

	M.

diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 43d212618834..fc95b103ef42 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -238,7 +238,7 @@ SYM_FUNC_START(switch_to_vhe)
 
 	// Turn the world upside down
 	mov	x0, #HVC_VHE_RESTART
-	hvc	#0
+//	hvc	#0
 1:
 	ret
 SYM_FUNC_END(switch_to_vhe)

-- 
Without deviation from the norm, progress is not possible.