On Mon, Aug 05, 2024 at 08:17:05AM -0700, Roman Kisel wrote: > > > On 8/4/2024 8:53 PM, Saurabh Singh Sengar wrote: > >On Fri, Jul 26, 2024 at 03:59:04PM -0700, Roman Kisel wrote: > >>The arm64 Hyper-V startup path relies on ACPI to detect > >>running under a Hyper-V compatible hypervisor. That > >>doesn't work on non-ACPI systems. > >> > >>Hoist the ACPI detection logic into a separate function, > >>use the new SMC added recently to Hyper-V to use in the > >>non-ACPI case. > >> > >>Signed-off-by: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx> > >>--- > >> arch/arm64/hyperv/mshyperv.c | 36 ++++++++++++++++++++++++++----- > >> arch/arm64/include/asm/mshyperv.h | 5 +++++ > >> 2 files changed, 36 insertions(+), 5 deletions(-) > >> > >>diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c > >>index b1a4de4eee29..341f98312667 100644 > >>--- a/arch/arm64/hyperv/mshyperv.c > >>+++ b/arch/arm64/hyperv/mshyperv.c > >>@@ -27,6 +27,34 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info) > >> return 0; > >> } > >>+static bool hyperv_detect_via_acpi(void) > >>+{ > >>+ if (acpi_disabled) > >>+ return false; > >>+#if IS_ENABLED(CONFIG_ACPI) > >>+ /* Hypervisor ID is only available in ACPI v6+. */ > >>+ if (acpi_gbl_FADT.header.revision < 6) > >>+ return false; > >>+ return strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8) == 0; > >>+#else > >>+ return false; > >>+#endif > >>+} > >>+ > >>+static bool hyperv_detect_via_smc(void) > >>+{ > >>+ struct arm_smccc_res res = {}; > >>+ > >>+ if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC) > >>+ return false; > >>+ arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res); > >>+ > >>+ return res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 && > >>+ res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 && > >>+ res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 && > >>+ res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3; > >>+} > > > >As you mentioned in the cover letter this is supported in latest Hyper-V hypervisor, > >can we add a comment about it, specifying the exact version in it would be great. > > > I can add a comment about that, thought that would look as too much > detail to refer to a version of the Windows insiders build in the > comments in this code. Another option would be to entrench the logic > in if statements which felt gross as there is a fallback. I'll leave the decision to your judgment. > > >If someone attempts to build non-ACPI kernel on older Hyper-V what is the > >behaviour of this function, do we need to safeguard or handle that case ? > The function won't panic if that's what you're asking about, i.e. > safe for runtime. That won't break the build either as it relies on > the SMCCC spec, and that uses the smc or hvc instructions (the code > does expect hvc to be the conduit and checks for that being the > case). The hypervisor doesn't inject the exception in the guest for > the unknown call, just returns SMCCC_RET_NOT_SUPPORTED in the first > output register (the hypervisor got a unit-test for that, too). Looks good, have you considered checking for SMCCC_RET_NOT_SUPPORTED ? - Saurabh