On 8/5/2024 8:46 AM, Saurabh Singh Sengar wrote:
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 ?
No, I have not. Let me think out loud here... `a0` is compared to what
must be return from the hypervisor the UID. That constant is an all-1 32
or 64 bit pattern, high unlikely to see that as a part of the UID due to
low entropy as I understand. I might've added the check though for the
better code readability, and because we have this e-mail thread going
on, looks like I must :) Let me do that in v4, thanks!
- Saurabh
--
Thank you,
Roman
