It appears that some drivers have to jump through a lot of hoops
to initialise correctly when running under a particular hypervisor,
while they can directly do it when running bare-metal.
Unfortunately, said hypervisor cannot be directly identified as it
doesn't implement the correct SMCCC interface, leaving the driver
with a certain amount of guesswork.
Being booted at EL2 provides at least an indication that there is no
non-nesting hypervisor, which is good enough to discriminate the
humpy hypervisor.
For this purpose, expose a new system-wide CPU capability aptly named
ARM64_HAS_EL2_OWNERSHIP, which said driver can check.
Note that this doesn't solve the problem of a kernel booted at EL1
without a hypervisor, or with a hypervisor that doesn't break the
device programming interface.
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/kernel/cpufeature.c | 11 +++++++++++
arch/arm64/tools/cpucaps | 1 +
2 files changed, 12 insertions(+)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 36c7b29ddf9e8..8fdc3ef23d9dc 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1868,6 +1868,11 @@ static bool has_nv1(const struct arm64_cpu_capabilities *entry, int scope)
is_midr_in_range_list(read_cpuid_id(), nv1_ni_list)));
}
+static bool has_el2_ownership(const struct arm64_cpu_capabilities *entry, int scope)
+{
+ return is_hyp_mode_available();
+}
+
#if defined(ID_AA64MMFR0_EL1_TGRAN_LPA2) && defined(ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_LPA2)
static bool has_lpa2_at_stage1(u64 mmfr0)
{
@@ -3012,6 +3017,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
ARM64_CPUID_FIELDS(ID_AA64PFR1_EL1, GCS, IMP)
},
#endif
+ {
+ .desc = "Kernel owns EL2",
+ .capability = ARM64_HAS_EL2_OWNERSHIP,
+ .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .matches = has_el2_ownership,
+ },
{},
};
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 1e65f2fb45bd1..94ce3462e6298 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -24,6 +24,7 @@ HAS_DIT
HAS_E0PD
HAS_ECV
HAS_ECV_CNTPOFF
+HAS_EL2_OWNERSHIP
HAS_EPAN
HAS_EVT
HAS_FPMR
--
2.39.2
--
Without deviation from the norm, progress is not possible.
