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Date:   Thu, 4 May 2023 18:58:14 +0300
From:   Zhi Wang <zhi.wang.linux@gmail.com>
To:     Tianyu Lan <ltykernel@gmail.com>
Cc:     luto@kernel.org, tglx@linutronix.de, mingo@redhat.com,
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        linux-arch@vger.kernel.org
Subject: Re: [RFC PATCH V5 03/15] x86/hyperv: Set Virtual Trust Level in
 VMBus init message
Message-ID: <20230504185814.00005792.zhi.wang.linux@gmail.com>
In-Reply-To: <4db13429-ffb0-debc-cec4-e37d0e526934@gmail.com>
References: <20230501085726.544209-1-ltykernel@gmail.com>
        <20230501085726.544209-4-ltykernel@gmail.com>
        <20230502223041.00000240.zhi.wang.linux@gmail.com>
        <4db13429-ffb0-debc-cec4-e37d0e526934@gmail.com>
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On Thu, 4 May 2023 08:38:46 -0700
Tianyu Lan <ltykernel@gmail.com> wrote:

> On 5/2/2023 12:30 PM, Zhi Wang wrote:
> > On Mon,  1 May 2023 04:57:13 -0400
> > Tianyu Lan <ltykernel@gmail.com> wrote:
> > 
> >> From: Tianyu Lan <tiala@microsoft.com>
> >>
> >> sev-snp guest provides vtl(Virtual Trust Level) and
> >> get it from hyperv hvcall via HVCALL_GET_VP_REGISTERS.
> >> Set target vtl in the VMBus init message.
> >>
> >> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> >> ---
> >> Change since RFC v4:
> >>         * Use struct_size to calculate array size.
> >>         * Fix some coding style
> >>
> >> Change since RFC v3:
> >>         * Use the standard helper functions to check hypercall result
> >>         * Fix coding style
> >>
> >> Change since RFC v2:
> >>         * Rename get_current_vtl() to get_vtl()
> >>         * Fix some coding style issues
> >> ---
> >>   arch/x86/hyperv/hv_init.c          | 36 ++++++++++++++++++++++++++++++
> >>   arch/x86/include/asm/hyperv-tlfs.h |  7 ++++++
> >>   drivers/hv/connection.c            |  1 +
> >>   include/asm-generic/mshyperv.h     |  1 +
> >>   include/linux/hyperv.h             |  4 ++--
> >>   5 files changed, 47 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> >> index 9f3e2d71d015..331b855314b7 100644
> >> --- a/arch/x86/hyperv/hv_init.c
> >> +++ b/arch/x86/hyperv/hv_init.c
> >> @@ -384,6 +384,40 @@ static void __init hv_get_partition_id(void)
> >>   	local_irq_restore(flags);
> >>   }
> >>   
> >> +static u8 __init get_vtl(void)
> >> +{
> >> +	u64 control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_REGISTERS;
> >> +	struct hv_get_vp_registers_input *input;
> >> +	struct hv_get_vp_registers_output *output;
> >> +	u64 vtl = 0;
> >> +	u64 ret;
> >> +	unsigned long flags;
> >> +
> >> +	local_irq_save(flags);
> >> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> >> +	output = (struct hv_get_vp_registers_output *)input;
> > 
> > ===
> >> +	if (!input) {
> >> +		local_irq_restore(flags);
> >> +		goto done;
> >> +	}
> >> +
> > ===
> > Is this really necessary?
> > 
> > drivers/hv/hv_common.c:
> > 
> >          hyperv_pcpu_input_arg = alloc_percpu(void  *);
> >          BUG_ON(!hyperv_pcpu_input_arg);
> > 
> > 
> 
> Hi Zhi:
> 	The hyperv_pcpu_input_arg is a point to address of input arg
> pages and these pages are allocated in the hv_common_cpu_init(). If
> it failed to allocate these pages, the value pointed by 
> hyperv_pcpu_input_arg will be NULL.
> 	

Sorry, it seems my email editor dropped some text. I was wondering that
if the check above is necessary as there is a BUG_ON() when allocating
hyperv_pcpu_input_arg.

So when coming to get_vtl(), the hyperv_pcpu_input_arg should not be NULL.
(Guarded by the BUG_ON() in the allocation)?