linux-kernel - Re: [PATCH v3 4/7] KVM: SVM: hyper-v: Nested enlightenments in VMCB

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Date:   Sun, 25 Apr 2021 09:30:39 -0400
From:   Vineeth Pillai <viremana@...ux.microsoft.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Lan Tianyu <Tianyu.Lan@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Wei Liu <wei.liu@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        viremana@...ux.microsoft.com
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "K. Y. Srinivasan" <kys@...rosoft.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Subject: Re: [PATCH v3 4/7] KVM: SVM: hyper-v: Nested enlightenments in VMCB

Hi Tom,


>>   
>> +
>> +#if IS_ENABLED(CONFIG_HYPERV)
>> +struct __packed hv_enlightenments {
>> +	struct __packed hv_enlightenments_control {
>> +		u32 nested_flush_hypercall:1;
>> +		u32 msr_bitmap:1;
>> +		u32 enlightened_npt_tlb: 1;
>> +		u32 reserved:29;
>> +	} hv_enlightenments_control;
>> +	u32 hv_vp_id;
>> +	u64 hv_vm_id;
>> +	u64 partition_assist_page;
>> +	u64 reserved;
>> +};
>> +#define VMCB_CONTROL_END	992	// 32 bytes for Hyper-V
>> +#else
>> +#define VMCB_CONTROL_END	1024
>> +#endif
>> +
>>   struct vmcb {
>>   	struct vmcb_control_area control;
>> -	u8 reserved_control[1024 - sizeof(struct vmcb_control_area)];
>> +	u8 reserved_control[VMCB_CONTROL_END - sizeof(struct vmcb_control_area)];
>> +#if IS_ENABLED(CONFIG_HYPERV)
>> +	struct hv_enlightenments hv_enlightenments;
>> +#endif
> I believe the 32 bytes at the end of the VMCB control area will be for use
> by any software/hypervisor. The APM update that documents this change,
> along with clean bit 31, isn't public, yet, but should be in a month or so
> (from what I was told).
>
> So these fields should be added generically and then your code should make
> use of the generic field mapped with your structure.
>
> To my knowledge (until the APM is public and documents everything), I
> believe the following will be in place:
>
>    VMCB offset 0x3e0 - 0x3ff is reserved for software
>    Clean bit 31 is reserved for software
>    SVM intercept exit code 0xf0000000 is reserved for software

Thanks for the details. I shall modify the code to accommodate this.


>   
> +#if IS_ENABLED(CONFIG_HYPERV)
> +	if (hypervisor_is_type(X86_HYPER_MS_HYPERV))
> +		vmcb_all_clean_mask |= BIT(VMCB_HV_NESTED_ENLIGHTENMENTS);
> +#endif
> +
> Is there any way to hide all the #if's in this and the other patches so
> that the .c files are littered with the #if IS_ENABLED() lines. Put them
> in svm.h or a new svm-hv.h file?

Will do.


>
>>   			  */
>>   	VMCB_DIRTY_MAX,
>> +#if IS_ENABLED(CONFIG_HYPERV)
>> +	VMCB_HV_NESTED_ENLIGHTENMENTS = 31,
>> +#endif
> Again, this should be generic.
Will do.

Thanks,
Vineeth