linux-kernel - Re: [PATCH 4/5] arm64: Warn on booting at EL2 with HVC disabled

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Date:   Thu, 12 Aug 2021 21:58:06 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com, kernel-team@...roid.com
Subject: Re: [PATCH 4/5] arm64: Warn on booting at EL2 with HVC disabled

On 12.08.2021 21:02, Marc Zyngier wrote:
> Now that we are able to paper over the gigantic stupidity that
> booting at EL2 with SCR_EL3.HCE==0 is, let's taint WARN_TAINT()
> when detecting this situation.
> 
> Yes, this is *LOUD*.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>

Tested-by: Rafał Miłecki <rafal@...ecki.pl>

This replaces:
CPU: All CPU(s) started at EL1

with:
------------[ cut here ]------------
CPU: CPUs downgraded to EL1, HVC disabled
WARNING: CPU: 0 PID: 1 at arch/arm64/kernel/smp.c:429 smp_cpus_done+0xac/0xe8
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.14.0-rc5-g86fc10657896 #41
Hardware name: Asus GT-AC5300 (DT)
pstate: 60000005 (nZCv daif -PAN -UAO -TCO BTYPE=--)
pc : smp_cpus_done+0xac/0xe8
lr : smp_cpus_done+0xac/0xe8
sp : ffffffc01002be00
x29: ffffffc01002be00 x28: 0000000000000000 x27: 0000000000000000
x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
x23: ffffffc010ab4000 x22: 0000000000000000 x21: 0000000000000000
x20: ffffffc0107b7e74 x19: ffffffc010a78000 x18: 0000000000000001
x17: ffffffc010a9ee40 x16: 0000000000000000 x15: 000042496b0a18f2
x14: fffffffffffc0f87 x13: 0000000000000039 x12: ffffff80010b03b0
x11: 00000000ffffffea x10: ffffffc010a5eb50 x9 : 0000000000000001
x8 : 0000000000000001 x7 : 0000000000017fe8 x6 : c0000000ffffefff
x5 : 0000000000057fa8 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 00000000ffffffff x1 : a8d68d1fd96fdc00 x0 : 0000000000000000
Call trace:
  smp_cpus_done+0xac/0xe8
  smp_init+0x68/0x78
  kernel_init_freeable+0xd0/0x214
  kernel_init+0x24/0x120
  ret_from_fork+0x10/0x18
---[ end trace a7d4af835e9d6e6b ]---


BEFORE:

smp: Bringing up secondary CPUs ...
Detected VIPT I-cache on CPU1
CPU1: Booted secondary processor 0x0000000001 [0x420f1000]
Detected VIPT I-cache on CPU2
CPU2: Booted secondary processor 0x0000000002 [0x420f1000]
Detected VIPT I-cache on CPU3
CPU3: Booted secondary processor 0x0000000003 [0x420f1000]
smp: Brought up 1 node, 4 CPUs
SMP: Total of 4 processors activated.
CPU features: detected: 32-bit EL0 Support
CPU features: detected: 32-bit EL1 Support
CPU features: detected: CRC32 instructions
CPU: All CPU(s) started at EL1


AFTER:

smp: Bringing up secondary CPUs ...
Detected VIPT I-cache on CPU1
CPU1: Booted secondary processor 0x0000000001 [0x420f1000]
Detected VIPT I-cache on CPU2
CPU2: Booted secondary processor 0x0000000002 [0x420f1000]
Detected VIPT I-cache on CPU3
CPU3: Booted secondary processor 0x0000000003 [0x420f1000]
smp: Brought up 1 node, 4 CPUs
SMP: Total of 4 processors activated.
CPU features: detected: 32-bit EL0 Support
CPU features: detected: 32-bit EL1 Support
CPU features: detected: CRC32 instructions
------------[ cut here ]------------
CPU: CPUs downgraded to EL1, HVC disabled
WARNING: CPU: 0 PID: 1 at arch/arm64/kernel/smp.c:429 smp_cpus_done+0xac/0xe8
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.14.0-rc5-g86fc10657896 #41
Hardware name: Asus GT-AC5300 (DT)
pstate: 60000005 (nZCv daif -PAN -UAO -TCO BTYPE=--)
pc : smp_cpus_done+0xac/0xe8
lr : smp_cpus_done+0xac/0xe8
sp : ffffffc01002be00
x29: ffffffc01002be00 x28: 0000000000000000 x27: 0000000000000000
x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
x23: ffffffc010ab4000 x22: 0000000000000000 x21: 0000000000000000
x20: ffffffc0107b7e74 x19: ffffffc010a78000 x18: 0000000000000001
x17: ffffffc010a9ee40 x16: 0000000000000000 x15: 000042496b0a18f2
x14: fffffffffffc0f87 x13: 0000000000000039 x12: ffffff80010b03b0
x11: 00000000ffffffea x10: ffffffc010a5eb50 x9 : 0000000000000001
x8 : 0000000000000001 x7 : 0000000000017fe8 x6 : c0000000ffffefff
x5 : 0000000000057fa8 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 00000000ffffffff x1 : a8d68d1fd96fdc00 x0 : 0000000000000000
Call trace:
  smp_cpus_done+0xac/0xe8
  smp_init+0x68/0x78
  kernel_init_freeable+0xd0/0x214
  kernel_init+0x24/0x120
  ret_from_fork+0x10/0x18
---[ end trace a7d4af835e9d6e6b ]---