From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Upton Date: Fri, 03 Feb 2023 21:08:00 +0000 Subject: Re: [RFC PATCH 29/32] KVM: arm64: Pass hypercalls to userspace Message-Id: List-Id: References: <20230203135043.409192-1-james.morse@arm.com> <20230203135043.409192-30-james.morse@arm.com> In-Reply-To: <20230203135043.409192-30-james.morse@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: James Morse Cc: linux-pm@vger.kernel.org, loongarch@lists.linux.dev, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, Marc Zyngier , Thomas Gleixner , Lorenzo Pieralisi , Mark Rutland , Sudeep Holla , Borislav Petkov , H Peter Anvin , Dave Hansen , Ingo Molnar , Will Deacon , Catalin Marinas , Huacai Chen , Suzuki K Poulose , Len Brown , Rafael Wysocki , WANG Xuerui , Salil Mehta , Russell King , Jean-Philippe Brucker Hi James, On Fri, Feb 03, 2023 at 01:50:40PM +0000, James Morse wrote: > From: Jean-Philippe Brucker > > When capability KVM_CAP_ARM_HVC_TO_USER is available, userspace can > request to handle all hypercalls that aren't handled by KVM. I would very much prefer we not go down this route. This capability effectively constructs an ABI out of what KVM presently does not implement. What would happen if KVM decides to implement a new set of hypercalls later down the road that were previously forwarded to userspace? Instead of a catch-all I think we should take the approach of having userspace explicitly request which hypercalls should be forwarded to userspace. I proposed something similar [1], but never got around to respinning it (oops). Let me dust those patches off and align with Marc's suggestions. [1]: https://lore.kernel.org/kvmarm/20221110015327.3389351-1-oliver.upton@linux.dev/ -- Thanks, Oliver