x86/hyperv: Move required MSRs check to initial platform probing

BugLink: https://bugs.launchpad.net/bugs/1953731
[ 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>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 49bb67595a2600cb57df70e19065d2c935ea2d75..934606f29294545b4c551b5351fd5b35be92635d 100644 (file)
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -356,20 +356,13 @@ 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 e095c28d27ae8468f16d7c90fed32c1063f90fd1..ef6316fef99ff4280057ba65e045beb0b8a9e635 100644 (file)
--- 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)