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From: Florian Fainelli <f.fainelli@gmail.com>
To: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Cc: "Rafał Miłecki" <zajec5@gmail.com>,
	"Will Deacon" <will@kernel.org>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	bcm-kernel-feedback-list@broadcom.com, kernel-team@android.com
Subject: Re: [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions
Date: Sun, 15 Aug 2021 09:28:47 +0200	[thread overview]
Message-ID: <7ffa35bb-1f2c-19ff-fe4b-33267fba80e8@gmail.com> (raw)
In-Reply-To: <20210812190213.2601506-1-maz@kernel.org>



On 8/12/2021 9:02 PM, Marc Zyngier wrote:
> Anyone vaguely familiar with the ARMv8 architecture would quickly
> understand that entering the kernel at EL2 without enabling the HVC
> instruction is... living dangerously. But as it turns out [0], there
> is a whole range of (*cough*) "high quality" (*cough*) Broadcom
> systems out there configured exactly like that.

Some Broadcom systems, namely the 4908 and all of those using CFE, they 
later switched to u-boot and ATF and got it right.

> 
> If you are speechless, I'm right with you.
> 
> These machines have stopped being able to boot an upstream kernel
> since 5.12, where we changed the way we switch from nVHE to VHE, as
> this relies on the HVC instruction being usable... It is also worth
> noting that these systems have never been able to use KVM. Or kexec.
> 
> This small series addresses the issue by detecting an UNDEFing HVC in
> a fairly controlled environment, and in this case pretend that we have
> booted at EL1. It also documents the requirement for SCR_EL3.HCE to be
> set to *1* if the kernel is entered at EL2. Turns out that we really
> have to state the obvious.
> 
> This has been tested on a FVP model with a hacked-up boot-wrapper.
> 
> Note that I really don't think any of this is -stable material, except
> maybe for the documentation. It isn't 5.14 material either. Best case,
> this is 5.15, or maybe even later. If ever.

While I am very appreciative of the work you have done here to try to 
get the dysfunctional systems to warn and continue to boot, I would 
rather we try to load a minimal shim at EL3 capable of fixing up any 
incorrect EL3 register setting ahead of loading the kernel provided this 
is possible at all on a commercially available system. Rafal, is this 
something that CFE allows you to do (as I could not get a straight 
answer from that team), if so have you tried it?
-- 
Florian

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WARNING: multiple messages have this Message-ID (diff)
From: Florian Fainelli <f.fainelli@gmail.com>
To: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Cc: "Rafał Miłecki" <zajec5@gmail.com>,
	"Will Deacon" <will@kernel.org>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	bcm-kernel-feedback-list@broadcom.com, kernel-team@android.com
Subject: Re: [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions
Date: Sun, 15 Aug 2021 09:28:47 +0200	[thread overview]
Message-ID: <7ffa35bb-1f2c-19ff-fe4b-33267fba80e8@gmail.com> (raw)
In-Reply-To: <20210812190213.2601506-1-maz@kernel.org>



On 8/12/2021 9:02 PM, Marc Zyngier wrote:
> Anyone vaguely familiar with the ARMv8 architecture would quickly
> understand that entering the kernel at EL2 without enabling the HVC
> instruction is... living dangerously. But as it turns out [0], there
> is a whole range of (*cough*) "high quality" (*cough*) Broadcom
> systems out there configured exactly like that.

Some Broadcom systems, namely the 4908 and all of those using CFE, they 
later switched to u-boot and ATF and got it right.

> 
> If you are speechless, I'm right with you.
> 
> These machines have stopped being able to boot an upstream kernel
> since 5.12, where we changed the way we switch from nVHE to VHE, as
> this relies on the HVC instruction being usable... It is also worth
> noting that these systems have never been able to use KVM. Or kexec.
> 
> This small series addresses the issue by detecting an UNDEFing HVC in
> a fairly controlled environment, and in this case pretend that we have
> booted at EL1. It also documents the requirement for SCR_EL3.HCE to be
> set to *1* if the kernel is entered at EL2. Turns out that we really
> have to state the obvious.
> 
> This has been tested on a FVP model with a hacked-up boot-wrapper.
> 
> Note that I really don't think any of this is -stable material, except
> maybe for the documentation. It isn't 5.14 material either. Best case,
> this is 5.15, or maybe even later. If ever.

While I am very appreciative of the work you have done here to try to 
get the dysfunctional systems to warn and continue to boot, I would 
rather we try to load a minimal shim at EL3 capable of fixing up any 
incorrect EL3 register setting ahead of loading the kernel provided this 
is possible at all on a commercially available system. Rafal, is this 
something that CFE allows you to do (as I could not get a straight 
answer from that team), if so have you tried it?
-- 
Florian

  parent reply	other threads:[~2021-08-15  7:31 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-12 19:02 [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions Marc Zyngier
2021-08-12 19:02 ` Marc Zyngier
2021-08-12 19:02 ` [PATCH 1/5] arm64: Directly expand __init_el2_nvhe_prepare_eret where needed Marc Zyngier
2021-08-12 19:02   ` Marc Zyngier
2021-08-12 19:02 ` [PATCH 2/5] arm64: Handle UNDEF in the EL2 stub vectors Marc Zyngier
2021-08-12 19:02   ` Marc Zyngier
2021-08-13 13:08   ` Robin Murphy
2021-08-13 13:08     ` Robin Murphy
2021-08-13 17:41     ` Marc Zyngier
2021-08-13 17:41       ` Marc Zyngier
2021-08-13 18:17       ` Robin Murphy
2021-08-13 18:17         ` Robin Murphy
2021-08-14  9:38         ` Marc Zyngier
2021-08-14  9:38           ` Marc Zyngier
2021-08-12 19:02 ` [PATCH 3/5] arm64: Detect disabled HVC early Marc Zyngier
2021-08-12 19:02   ` Marc Zyngier
2021-08-12 19:47   ` Rafał Miłecki
2021-08-12 19:47     ` Rafał Miłecki
2021-08-13  9:05   ` Will Deacon
2021-08-13  9:05     ` Will Deacon
2021-08-13 17:33     ` Marc Zyngier
2021-08-13 17:33       ` Marc Zyngier
2021-08-12 19:02 ` [PATCH 4/5] arm64: Warn on booting at EL2 with HVC disabled Marc Zyngier
2021-08-12 19:02   ` Marc Zyngier
2021-08-12 19:58   ` Rafał Miłecki
2021-08-12 19:58     ` Rafał Miłecki
2021-08-12 19:02 ` [PATCH 5/5] arm64: Document the requirement for SCR_EL3.HCE Marc Zyngier
2021-08-12 19:02   ` Marc Zyngier
2021-08-24 10:49   ` Catalin Marinas
2021-08-24 10:49     ` Catalin Marinas
2021-08-24 10:52     ` Mark Rutland
2021-08-24 10:52       ` Mark Rutland
2021-08-15  7:28 ` Florian Fainelli [this message]
2021-08-15  7:28   ` [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions Florian Fainelli
2021-08-15  9:27   ` Marc Zyngier
2021-08-15  9:27     ` Marc Zyngier
2021-08-22 11:31     ` Florian Fainelli
2021-08-22 11:31       ` Florian Fainelli
2021-08-24 16:19 ` (subset) " Catalin Marinas
2021-08-24 16:19   ` Catalin Marinas

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