linux-kernel - Re: [PATCH 0/2] Add support for Gunyah Watchdog

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250904001014.GA3405605-robh@kernel.org>
Date: Wed, 3 Sep 2025 19:10:14 -0500
From: Rob Herring <robh@...nel.org>
To: Hrishabh Rajput <hrishabh.rajput@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Wim Van Sebroeck <wim@...ux-watchdog.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
	linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Add support for Gunyah Watchdog

On Wed, Sep 03, 2025 at 07:33:58PM +0000, Hrishabh Rajput wrote:
> Gunyah is a Type-I hypervisor which was introduced in the patch series
> [1]. It is an open source hypervisor. The source repo is available at
> [2].
> 
> The Gunyah Hypervisor doesn't allow its Virtual Machines to directly
> access the MMIO watchdog. It either provides the fully emulated MMIO
> based watchdog interface or the SMC-based watchdog interface depending
> on the hypervisor configuration.

EFI provides a standard watchdog interface. Why can't you use that?

> The SMC-based watchdog follows ARM's SMC Calling Convention (SMCCC)
> version 1.1 and uses Vendor Specific Hypervisor Service Calls space.

Is a watchdog really a hypervisor service? Couldn't a non-virtualized 
OS want to call a watchdog (in secure mode) as well? But I don't know 
how the SMCCC call space is divided up...

> This patch series adds support for the SMC-based watchdog interface
> provided by the Gunyah Hypervisor. The driver supports start/stop
> operations, timeout and pretimeout configuration, pretimeout interrupt
> handling and system restart via watchdog.

Shouldn't system restart be handled by PSCI?

Why can't you probe by trying to see if watchdog smc call succeeds to 
see if there is a watchdog? Then you don't need DT for it.
 
Rob