2023-09-20 07:47:50

by Saurabh Sengar

Subject: [PATCH v3] 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 <[email protected]>
Reviewed-by: Vitaly Kuznetsov <[email protected]>
---
[V3]
- Modified commit message
- Added reviewed-by

[V2]
- Put the if else at function definition rather then at the caller

arch/x86/hyperv/hv_init.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 783ed339f341..f0128fd4031d 100644
--- 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 @@ void __init hyperv_init(void)
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;

--
2.34.1

2023-09-22 18:48:09

by Wei Liu

Subject: Re: [PATCH v3] x86/hyperv: Restrict get_vtl to only VTL platforms

On Tue, Sep 19, 2023 at 09:04:35PM -0700, Saurabh Sengar wrote:
> 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 <[email protected]>
> Reviewed-by: Vitaly Kuznetsov <[email protected]>

Applied to hyperv-fixes. Thanks.