linux-kernel - Re: [PATCH v2 1/4] x86/vmware: Update platform detection code for VMCALL/VMMCALL hypercalls

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Date:   Tue, 27 Aug 2019 21:19:54 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, pv-drivers@...are.com,
        linux-graphics-maintainer@...are.com,
        Thomas Hellstrom <thellstrom@...are.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        dri-devel@...ts.freedekstop.org, Doug Covelli <dcovelli@...are.com>
Subject: Re: [PATCH v2 1/4] x86/vmware: Update platform detection code for
 VMCALL/VMMCALL hypercalls

Thanks for reviewing, Borislav. Comments inline.

On 8/27/19 2:56 PM, Borislav Petkov wrote:

> On Fri, Aug 23, 2019 at 10:13:13AM +0200, Thomas Hellström (VMware) wrote:
>
>> +
>> +#define VMWARE_CMD(cmd, eax, ebx, ecx, edx) do {		\
>> +	switch (vmware_hypercall_mode) {			\
>> +	case CPUID_VMWARE_FEATURES_ECX_VMCALL:			\
>> +		VMWARE_VMCALL(cmd, eax, ebx, ecx, edx);		\
>> +		break;						\
>> +	case CPUID_VMWARE_FEATURES_ECX_VMMCALL:			\
>> +		VMWARE_VMMCALL(cmd, eax, ebx, ecx, edx);	\
>> +		break;						\
>> +	default:						\
> Please integrate scripts/checkpatch.pl into your patch creation
> workflow. Some of the warnings/errors *actually* make sense:
>
> WARNING: Possible switch case/default not preceded by break or fallthrough comment
> #110: FILE: arch/x86/kernel/cpu/vmware.c:81:
> +       case CPUID_VMWARE_FEATURES_ECX_VMMCALL:                 \
>
> WARNING: Possible switch case/default not preceded by break or fallthrough comment
> #113: FILE: arch/x86/kernel/cpu/vmware.c:84:
> +       default:
>
> In this case, we're going to enable -Wimplicit-fallthrough by default at
> some point.

We *do* have checkpatch.pl in the workflow. In this case I figured the 
warnings actually didn't make sense. There are breaks present and 
-Wimplicit-fallthrough doesn't complain...


	(unsigned int) vmware_hypercall_mode);

> Is that supposed to be debug output? If so, pr_dbg().

This is intentionally intended to be part of the initial output.

>
>> +
>>   			return CPUID_VMWARE_INFO_LEAF;
>> +		}
>>   	} else if (dmi_available && dmi_name_in_serial("VMware") &&
>>   		   __vmware_platform())
> What sets vmware_hypercall_mode in this case? Or is the 0 magic to mean,
> use the default: VMWARE_PORT inl call?

Yes, Perhaps I should add a comment about that.

>
> Also, you could restructure that function something like this to save yourself
> an indentation level or two and make it more easily readable:
>
> static uint32_t __init vmware_platform(void)
> {
>          unsigned int hyper_vendor_id[3];
>          unsigned int eax;
>
>          if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
>                  if (dmi_available && dmi_name_in_serial("VMware") && __vmware_platform())
>                          return 1;
>          }
>
>          cpuid(CPUID_VMWARE_INFO_LEAF, &eax, &hyper_vendor_id[0],
>                &hyper_vendor_id[1], &hyper_vendor_id[2]);
>
>          if (!memcmp(hyper_vendor_id, "VMwareVMware", 12)) {
>                  if (eax >= CPUID_VMWARE_FEATURES_LEAF)
>                          vmware_hypercall_mode = vmware_select_hypercall();
>
>                  pr_info("hypercall mode: 0x%02x\n", (unsigned int) vmware_hypercall_mode);
>
>                  return CPUID_VMWARE_INFO_LEAF;
>          }
>          return 0;
> }
>
Sure, I'll add that as a separate patch.

For the other comments, I'll fix up and respin.

Thanks,

Thomas