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
