Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH 3/5] arm64: Detect disabled HVC early
To:     Marc Zyngier <maz@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     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
References: <20210812190213.2601506-1-maz@kernel.org>
 <20210812190213.2601506-4-maz@kernel.org>
From:   =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>
Message-ID: <11c7b042-885f-ad48-7c5f-ad3dbd8f0340@gmail.com>
Date:   Thu, 12 Aug 2021 21:47:18 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.1
MIME-Version: 1.0
In-Reply-To: <20210812190213.2601506-4-maz@kernel.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 12.08.2021 21:02, Marc Zyngier wrote:
> Having HVC disabled from EL3 while the kernel is entered at EL2
> is a complete nightmare.
> 
> We end-up taking an UNDEF at the worse possible moment (checking
> for VHE) and even if we didn't, having KVM enabled would signify
> the premature end of the kernel.
> 
> Instead, try and detect this stupid case by issuing a HVC
> for HVC_RESET_VECTORS, which does nothing when the stubs
> are live. If we get HVC_STUB_ERR back, that's because the
> UNDEF handler has kicked in.
> 
> In this situation, close your eyes, block your nose, and gracefully
> pretend we have booted at EL1.
> 
> Reported-by: Rafał Miłecki <zajec5@gmail.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>

This does the trick.

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