[PATCH 5.15 020/207] x86/hyperv: Move required MSRs check to initial platform probing

Greg Kroah-Hartman
2021-12-06T15:32:49Z

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit f3e613e72f66226b3bea1046c1b864f67a3000a4 ]

Explicitly check for MSR_HYPERCALL and MSR_VP_INDEX support when probing
for running as a Hyper-V guest instead of waiting until hyperv_init() to
detect the bogus configuration. Add messages to give the admin a heads
up that they are likely running on a broken virtual machine setup.

At best, silently disabling Hyper-V is confusing and difficult to debug,
e.g. the kernel _says_ it's using all these fancy Hyper-V features, but
always falls back to the native versions. At worst, the half baked setup
will crash/hang the kernel.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20211104182239.1302956-3-seanjc@google.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/hyperv/hv_init.c | 9 +--------
arch/x86/kernel/cpu/mshyperv.c | 20 +++++++++++++++-----
2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index d20eef3d452a5..b6d48ca5b0f17 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -348,20 +348,13 @@ static void __init hv_get_partition_id(void)
*/
void __init hyperv_init(void)
{
- u64 guest_id, required_msrs;
+ u64 guest_id;
union hv_x64_msr_hypercall_contents hypercall_msr;
int cpuhp;

if (x86_hyper_type != X86_HYPER_MS_HYPERV)
return;

- /* Absolutely required MSRs */
- required_msrs = HV_MSR_HYPERCALL_AVAILABLE |
- HV_MSR_VP_INDEX_AVAILABLE;
-
- if ((ms_hyperv.features & required_msrs) != required_msrs)
- return;
-
if (hv_common_init())
return;

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index e095c28d27ae8..ef6316fef99ff 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -163,12 +163,22 @@ static uint32_t __init ms_hyperv_platform(void)
cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS,
&eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]);

- if (eax >= HYPERV_CPUID_MIN &&
- eax <= HYPERV_CPUID_MAX &&
- !memcmp("Microsoft Hv", hyp_signature, 12))
- return HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
+ if (eax < HYPERV_CPUID_MIN || eax > HYPERV_CPUID_MAX ||
+ memcmp("Microsoft Hv", hyp_signature, 12))
+ return 0;

- return 0;
+ /* HYPERCALL and VP_INDEX MSRs are mandatory for all features. */
+ eax = cpuid_eax(HYPERV_CPUID_FEATURES);
+ if (!(eax & HV_MSR_HYPERCALL_AVAILABLE)) {
+ pr_warn("x86/hyperv: HYPERCALL MSR not available.\n");
+ return 0;
+ }
+ if (!(eax & HV_MSR_VP_INDEX_AVAILABLE)) {
+ pr_warn("x86/hyperv: VP_INDEX MSR not available.\n");
+ return 0;
+ }
+
+ return HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
}

static unsigned char hv_get_nmi_reason(void)
--
2.33.0