linux-kernel - Re: [PATCH v2 1/7] KVM:VMX: Define CET VMCS fields and bits

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Message-ID: <20190125223010.GA21849@linux.intel.com>
Date:   Fri, 25 Jan 2019 14:30:10 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
        yu-cheng.yu@...el.com, yi.z.zhang@...el.com, hjl.tools@...il.com,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v2 1/7] KVM:VMX: Define CET VMCS fields and bits

On Wed, Jan 23, 2019 at 04:59:03AM +0800, Yang Weijiang wrote:
> On processors that support CET, VMX saves/restores
> the states of IA32_S_CET, SSP and IA32_INTERRUPT_SSP_TABLE_ADDR MSR

It'd be helpful to spell out CET and SSP on their initial usage here,
especially since this is the first patch in the series.

If you're going to abbreviate INTERRUPT below, might as well do so here.

> to the VMCS area for Guest/Host unconditionally.
> 
> If VM_EXIT_LOAD_HOST_CET_STATE = 1, the host CET MSRs are
> restored from VMCS host-state area at VM exit as follows:
> 
> - HOST_IA32_S_CET: Host supervisor mode IA32_S_CET MSR is loaded
>                    from this field.
> 
> - HOST_SSP : Host SSP is loaded from this field.
> 
> - HOST_INTR_SSP_TABLE_ADDR : Host IA32_INTERRUPT_SSP_TABLE_ADDR
>                              MSR is loaded from this field.
> 
> If VM_ENTRY_LOAD_GUEST_CET_STATE = 1, the guest CET MSRs are loaded
> from VMCS guest-state area at VM entry as follows:
> 
> - GUEST_IA32_S_CET : Guest supervisor mode IA32_S_CET MSR is loaded
>                      from this field.
> 
> - GUEST_SSP : Guest SSP is loaded from this field.
> 
> - GUEST_INTR_SSP_TABL_ADDR : Guest IA32_INTERRUPT_SSP_TABLE_ADDR

/s/TABL_/TABLE_

>                              MSR is loaded from this field.
> 
> Additionally, to context switch guest and host CET states, the VMM
> uses xsaves/xrstors instructions to save/restore the guest CET states
> at VM exit/entry. The CET xsave area is within thread_struct.fpu area.
> If OS execution flow changes during task switch/interrupt/exception etc.,
> the OS also relies on xsaves/xrstors to switch CET states accordingly.
> 
> Note: Although these VMCS fields are 64-bit, they don't have high fields.

...that are documented.  I'm still betting it's a doc bug and not a
divergence from every other VMCS field in existence.

> Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/include/asm/vmx.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index ade0f153947d..395c1f7e5938 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -98,6 +98,7 @@
>  #define VM_EXIT_LOAD_IA32_EFER                  0x00200000
>  #define VM_EXIT_SAVE_VMX_PREEMPTION_TIMER       0x00400000
>  #define VM_EXIT_CLEAR_BNDCFGS                   0x00800000
> +#define VM_EXIT_LOAD_HOST_CET_STATE             0x10000000
>  
>  #define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR	0x00036dff
>  
> @@ -109,6 +110,7 @@
>  #define VM_ENTRY_LOAD_IA32_PAT			0x00004000
>  #define VM_ENTRY_LOAD_IA32_EFER                 0x00008000
>  #define VM_ENTRY_LOAD_BNDCFGS                   0x00010000
> +#define VM_ENTRY_LOAD_GUEST_CET_STATE           0x00100000
>  
>  #define VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR	0x000011ff
>  
> @@ -325,6 +327,9 @@ enum vmcs_field {
>  	GUEST_PENDING_DBG_EXCEPTIONS    = 0x00006822,
>  	GUEST_SYSENTER_ESP              = 0x00006824,
>  	GUEST_SYSENTER_EIP              = 0x00006826,
> +	GUEST_IA32_S_CET                = 0x00006828,
> +	GUEST_SSP                       = 0x0000682a,
> +	GUEST_INTR_SSP_TABL_ADDR        = 0x0000682c,

/s/TABL/TABLE

>  	HOST_CR0                        = 0x00006c00,
>  	HOST_CR3                        = 0x00006c02,
>  	HOST_CR4                        = 0x00006c04,
> @@ -337,6 +342,9 @@ enum vmcs_field {
>  	HOST_IA32_SYSENTER_EIP          = 0x00006c12,
>  	HOST_RSP                        = 0x00006c14,
>  	HOST_RIP                        = 0x00006c16,
> +	HOST_IA32_S_CET                 = 0x00006c18,
> +	HOST_SSP                        = 0x00006c1a,
> +	HOST_INTR_SSP_TABL_ADDR         = 0x00006c1c

/s/TABL/TABLE

>  };
>  
>  /*
> -- 
> 2.17.1
>