linux-kernel - Re: [PATCH] x86/Hyper-V: Expand definition of struct hv_vp_assist

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Message-ID: <20221104075142.GA6146@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date:   Fri, 4 Nov 2022 00:51:42 -0700
From:   Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To:     Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
Cc:     ssengar@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        mikelley@...rosoft.com, tglx@...utronix.de, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com
Subject: Re: [PATCH] x86/Hyper-V: Expand definition of struct
 hv_vp_assist_page

On Fri, Nov 04, 2022 at 12:46:57PM +0530, Anirudh Rayabharam wrote:
> On Thu, Nov 03, 2022 at 09:56:54PM -0700, Saurabh Sengar wrote:
> > The struct hv_vp_assist_page has 24 bytes which is defined as u64[3],
> > expand that to expose vtl_entry_reason, vtl_ret_x64rax and vtl_ret_x64rcx
> > field. vtl_entry_reason is updated by hypervisor for the entry reason as
> > to why the VTL was entered on the virtual processor.
> > Guest updates the vtl_ret_* fields to provide the register values to
> > restore on VTL return. The specific register values that are restored
> > which will be updated on vtl_ret_x64rax and vtl_ret_x64rcx.
> > Also added the missing fields for synthetic_time_unhalted_timer_expired,
> > virtualization_fault_information and intercept_message.
> > 
> > Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> > ---
> >  arch/x86/include/asm/hyperv-tlfs.h | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> > index f769b9db4630..b3d0f42853d2 100644
> > --- a/arch/x86/include/asm/hyperv-tlfs.h
> > +++ b/arch/x86/include/asm/hyperv-tlfs.h
> > @@ -377,11 +377,20 @@ struct hv_nested_enlightenments_control {
> >  struct hv_vp_assist_page {
> >  	__u32 apic_assist;
> >  	__u32 reserved1;
> > -	__u64 vtl_control[3];
> > +	__u8  vtl_entry_reason;
> 
> This is defined as an enum in the TLFS [1]. We should do the same.
> And since the TLFS defines it as an enum it is a 32 bit value and
> not a u8.

I think we can do that. Let me check this and update on v2.

> 
> > +	__u8  vtl_reserved[7];
> > +	__u64 vtl_ret_x64rax;
> > +	__u64 vtl_ret_x64rcx;
> 
> The TLFS groups the above VTL related fields into a struct
> HV_VP_VTL_CONTROL. Any reason to not do the same?

No particular reason, but this change is simple and sufficient.
We can expand in future as the need arises.

> 
> [1] https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/datatypes/hv_vp_vtl_control
> 
> Thanks,
> Anirudh.
> 
> >  	struct hv_nested_enlightenments_control nested_control;
> >  	__u8 enlighten_vmentry;
> >  	__u8 reserved2[7];
> >  	__u64 current_nested_vmcs;
> > +	__u8 synthetic_time_unhalted_timer_expired;
> > +	__u8 reserved3[7];
> > +	__u8 virtualization_fault_information[40];
> > +	__u8 reserved4[8];
> > +	__u8 intercept_message[256];
> > +	__u8 vtl_ret_actions[256];
> >  } __packed;
> >  
> >  struct hv_enlightened_vmcs {
> > -- 
> > 2.34.1