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Mon, 10 Mar 2025 17:21:05 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 Date: Mon, 10 Mar 2025 22:20:41 +0100 From: "Arnd Bergmann" To: "Michael Kelley" , "Roman Kisel" , "bhelgaas@google.com" , "Borislav Petkov" , "Catalin Marinas" , "Conor Dooley" , "Dave Hansen" , "Dexuan Cui" , "Haiyang Zhang" , "H. Peter Anvin" , "Joey Gouly" , "krzk+dt@kernel.org" , =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= , "K. Y. Srinivasan" , "Len Brown" , "Lorenzo Pieralisi" , "Manivannan Sadhasivam" , "Mark Rutland" , "Marc Zyngier" , "Ingo Molnar" , "Oliver Upton" , "Rafael J . Wysocki" , "Rob Herring" , "ssengar@linux.microsoft.com" , "Sudeep Holla" , "Suzuki K Poulose" , "Thomas Gleixner" , "Wei Liu" , "Will Deacon" , "Zenghui Yu" , "devicetree@vger.kernel.org" , "kvmarm@lists.linux.dev" , "linux-acpi@vger.kernel.org" , Linux-Arch , "linux-arm-kernel@lists.infradead.org" , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-pci@vger.kernel.org" , "x86@kernel.org" Cc: "apais@microsoft.com" , "benhill@microsoft.com" , "bperkins@microsoft.com" , "sunilmut@microsoft.com" Message-Id: <119cfb59-d68b-4718-b7cb-90cba67827e8@app.fastmail.com> In-Reply-To: References: <20250307220304.247725-1-romank@linux.microsoft.com> <20250307220304.247725-4-romank@linux.microsoft.com> Subject: Re: [PATCH hyperv-next v5 03/11] Drivers: hv: Enable VTL mode for arm64 Content-Type: text/plain Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250310_142111_567892_5A2CA182 X-CRM114-Status: GOOD ( 17.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Mar 10, 2025, at 22:01, Michael Kelley wrote: > From: Arnd Bergmann Sent: Saturday, March 8, 2025 1:05 PM >> > config HYPERV_VTL_MODE >> > bool "Enable Linux to boot in VTL context" >> > - depends on X86_64 && HYPERV >> > + depends on (X86_64 || ARM64) >> > depends on SMP >> > + select OF_EARLY_FLATTREE >> > + select OF >> > default n >> > help >> >> Having the dependency below the top-level Kconfig entry feels a little >> counterintuitive. You could flip that back as it was before by doing >> >> select HYPERV_VTL_MODE if !ACPI >> depends on ACPI || SMP >> >> in the HYPERV option, leaving the dependency on HYPERV in >> HYPERV_VTL_MODE. > > I would argue that we don't ever want to implicitly select > HYPERV_VTL_MODE because of some other config setting or > lack thereof. VTL mode is enough of a special case that it should > only be explicitly selected. If someone omits ACPI, then HYPERV > should not be selectable unless HYPERV_VTL_MODE is explicitly > selected. > > The last line of the comment for HYPERV_VTL_MODE says > "A kernel built with this option must run at VTL2, and will not run > as a normal guest." In other words, don't choose this unless you > 100% know that VTL2 is what you want. It sounds like the latter is the real problem: enabling a feature should never prevent something else from working. Can you describe what VTL context is and why it requires an exception to a rather fundamental rule here? If you build a kernel that runs on every single piece of arm64 hardware and every hypervisor, why can't you add HYPERV_VTL_MODE to that as an option? Arnd