x86/hyperv: Restrict get_vtl to only VTL platforms

When Linux runs in a non-default VTL (CONFIG_HYPERV_VTL_MODE=y),
get_vtl() must never fail as its return value is used in negotiations
with the host. In the more generic case, (CONFIG_HYPERV_VTL_MODE=n) the
VTL is always zero so there's no need to do the hypercall.

Make get_vtl() BUG() in case of failure and put the implementation under
"if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)" to avoid the call altogether in
the most generic use case.

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/1695182675-13405-1-git-send-email-ssengar@linux.microsoft.com

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 783ed339f3415c09bf83830b0bd854d92e5f31dc..f0128fd4031de9002bb9d863aa5a6674df5a0a5d 100644 (file)
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -394,6 +394,7 @@ static void __init hv_get_partition_id(void)
        local_irq_restore(flags);
 }
 
+#if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
 static u8 __init get_vtl(void)
 {
        u64 control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_REGISTERS;
@@ -416,13 +417,16 @@ static u8 __init get_vtl(void)
        if (hv_result_success(ret)) {
                ret = output->as64.low & HV_X64_VTL_MASK;
        } else {
-               pr_err("Failed to get VTL(%lld) and set VTL to zero by default.\n", ret);
-               ret = 0;
+               pr_err("Failed to get VTL(error: %lld) exiting...\n", ret);
+               BUG();
        }
 
        local_irq_restore(flags);
        return ret;
 }
+#else
+static inline u8 get_vtl(void) { return 0; }
+#endif
 
 /*
  * This function is to be invoked early in the boot sequence after the
@@ -604,8 +608,7 @@ skip_hypercall_pg_init:
        hv_query_ext_cap(0);
 
        /* Find the VTL */
-       if (!ms_hyperv.paravisor_present && hv_isolation_type_snp())
-               ms_hyperv.vtl = get_vtl();
+       ms_hyperv.vtl = get_vtl();
 
        return;