RE: [PATCH v5 1/2] x86/vtx: add LBR_SELECT to the list of LBR MSRs

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> Sent: Thursday, April 15, 2021 6:04 PM
> 
> This MSR exists since Nehalem / Silvermont and is actively used by Linux,
> for instance, to improve sampling efficiency.
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

> ---
> Changes in v5:
> - added Silvermont+ LBR_SELECT support
> 
> New patch in v4 as suggested by Andrew.
> ---
>  xen/arch/x86/hvm/vmx/vmx.c      | 20 ++++++++++++++++----
>  xen/include/asm-x86/msr-index.h | 10 ++++++++--
>  2 files changed, 24 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 835b905..30c6a57 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -2915,14 +2915,16 @@ static const struct lbr_info {
>  }, nh_lbr[] = {
>      { MSR_IA32_LASTINTFROMIP,       1 },
>      { MSR_IA32_LASTINTTOIP,         1 },
> -    { MSR_C2_LASTBRANCH_TOS,        1 },
> +    { MSR_NHL_LBR_SELECT,           1 },
> +    { MSR_NHL_LASTBRANCH_TOS,       1 },
>      { MSR_P4_LASTBRANCH_0_FROM_LIP,
> NUM_MSR_P4_LASTBRANCH_FROM_TO },
>      { MSR_P4_LASTBRANCH_0_TO_LIP,
> NUM_MSR_P4_LASTBRANCH_FROM_TO },
>      { 0, 0 }
>  }, sk_lbr[] = {
>      { MSR_IA32_LASTINTFROMIP,       1 },
>      { MSR_IA32_LASTINTTOIP,         1 },
> -    { MSR_SKL_LASTBRANCH_TOS,       1 },
> +    { MSR_NHL_LBR_SELECT,           1 },
> +    { MSR_NHL_LASTBRANCH_TOS,       1 },
>      { MSR_SKL_LASTBRANCH_0_FROM_IP, NUM_MSR_SKL_LASTBRANCH },
>      { MSR_SKL_LASTBRANCH_0_TO_IP,   NUM_MSR_SKL_LASTBRANCH },
>      { MSR_SKL_LASTBRANCH_0_INFO,    NUM_MSR_SKL_LASTBRANCH },
> @@ -2934,10 +2936,19 @@ static const struct lbr_info {
>      { MSR_C2_LASTBRANCH_0_FROM_IP,
> NUM_MSR_ATOM_LASTBRANCH_FROM_TO },
>      { MSR_C2_LASTBRANCH_0_TO_IP,
> NUM_MSR_ATOM_LASTBRANCH_FROM_TO },
>      { 0, 0 }
> +}, sm_lbr[] = {
> +    { MSR_IA32_LASTINTFROMIP,       1 },
> +    { MSR_IA32_LASTINTTOIP,         1 },
> +    { MSR_SM_LBR_SELECT,            1 },
> +    { MSR_SM_LASTBRANCH_TOS,        1 },
> +    { MSR_C2_LASTBRANCH_0_FROM_IP,
> NUM_MSR_ATOM_LASTBRANCH_FROM_TO },
> +    { MSR_C2_LASTBRANCH_0_TO_IP,
> NUM_MSR_ATOM_LASTBRANCH_FROM_TO },
> +    { 0, 0 }
>  }, gm_lbr[] = {
>      { MSR_IA32_LASTINTFROMIP,       1 },
>      { MSR_IA32_LASTINTTOIP,         1 },
> -    { MSR_GM_LASTBRANCH_TOS,        1 },
> +    { MSR_SM_LBR_SELECT,            1 },
> +    { MSR_SM_LASTBRANCH_TOS,        1 },
>      { MSR_GM_LASTBRANCH_0_FROM_IP,
> NUM_MSR_GM_LASTBRANCH_FROM_TO },
>      { MSR_GM_LASTBRANCH_0_TO_IP,
> NUM_MSR_GM_LASTBRANCH_FROM_TO },
>      { 0, 0 }
> @@ -2991,6 +3002,7 @@ static const struct lbr_info
> *last_branch_msr_get(void)
>              return sk_lbr;
>          /* Atom */
>          case 0x1c: case 0x26: case 0x27: case 0x35: case 0x36:
> +            return at_lbr;
>          /* Silvermont */
>          case 0x37: case 0x4a: case 0x4d: case 0x5a: case 0x5d:
>          /* Xeon Phi Knights Landing */
> @@ -2999,7 +3011,7 @@ static const struct lbr_info
> *last_branch_msr_get(void)
>          case 0x85:
>          /* Airmont */
>          case 0x4c:
> -            return at_lbr;
> +            return sm_lbr;
>          /* Goldmont */
>          case 0x5c: case 0x5f:
>              return gm_lbr;
> diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-
> index.h
> index 43d26ef..020908f 100644
> --- a/xen/include/asm-x86/msr-index.h
> +++ b/xen/include/asm-x86/msr-index.h
> @@ -606,15 +606,21 @@
>  #define NUM_MSR_C2_LASTBRANCH_FROM_TO        4
>  #define NUM_MSR_ATOM_LASTBRANCH_FROM_TO      8
> 
> +/* Nehalem (and newer) last-branch recording */
> +#define MSR_NHL_LBR_SELECT           0x000001c8
> +#define MSR_NHL_LASTBRANCH_TOS               0x000001c9
> +
>  /* Skylake (and newer) last-branch recording */
> -#define MSR_SKL_LASTBRANCH_TOS               0x000001c9
>  #define MSR_SKL_LASTBRANCH_0_FROM_IP 0x00000680
>  #define MSR_SKL_LASTBRANCH_0_TO_IP   0x000006c0
>  #define MSR_SKL_LASTBRANCH_0_INFO    0x00000dc0
>  #define NUM_MSR_SKL_LASTBRANCH               32
> 
> +/* Silvermont (and newer) last-branch recording */
> +#define MSR_SM_LBR_SELECT            0x000001c8
> +#define MSR_SM_LASTBRANCH_TOS                0x000001c9
> +
>  /* Goldmont last-branch recording */
> -#define MSR_GM_LASTBRANCH_TOS                0x000001c9
>  #define MSR_GM_LASTBRANCH_0_FROM_IP  0x00000680
>  #define MSR_GM_LASTBRANCH_0_TO_IP    0x000006c0
>  #define NUM_MSR_GM_LASTBRANCH_FROM_TO        32
> --
> 2.7.4