Re: [PATCH 3/4] VMX: allow RTM advanced debugging to be used by guests

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 12/08/14 10:17, Jan Beulich wrote:
> All that is needed here is allowing the respective DebugCtl MSR bit to
> be set by the guest.
>
> At once - even if PV guests can't currently use it due to missing
> DebugCtl MSR virtualization - make the respective adjustments to
> debugreg.h.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -2246,6 +2246,8 @@ static int vmx_msr_write_intercept(unsig
>          int i, rc = 0;
>          uint64_t supported = IA32_DEBUGCTLMSR_LBR | IA32_DEBUGCTLMSR_BTF;
>  
> +        if ( boot_cpu_has(X86_FEATURE_RTM) )
> +            supported |= IA32_DEBUGCTLMSR_RTM;

This supported bitmask is runtime constant.  Is it worth precalculating
it, rather than reevaluating each time DEBUGCTL is written to?

~Andrew

>          if ( msr_content & ~supported )
>          {
>              /* Perhaps some other bits are supported in vpmu. */
> --- a/xen/include/asm-x86/debugreg.h
> +++ b/xen/include/asm-x86/debugreg.h
> @@ -20,6 +20,7 @@
>  #define DR_TRAP3        (0x8)           /* db3 */
>  #define DR_STEP         (0x4000)        /* single-step */
>  #define DR_SWITCH       (0x8000)        /* task switch */
> +#define DR_NOT_RTM      (0x10000)       /* clear: #BP inside RTM region */
>  
>  /* Now define a bunch of things for manipulating the control register.
>     The top two bytes of the control register consist of 4 fields of 4
> @@ -62,6 +63,7 @@
>  #define DR_CONTROL_RESERVED_ONE  (0x00000400ul) /* Reserved, read as one */
>  #define DR_LOCAL_EXACT_ENABLE    (0x00000100ul) /* Local exact enable */
>  #define DR_GLOBAL_EXACT_ENABLE   (0x00000200ul) /* Global exact enable */
> +#define DR_RTM_ENABLE            (0x00000800ul) /* RTM debugging enable */
>  #define DR_GENERAL_DETECT        (0x00002000ul) /* General detect enable */
>  
>  #define write_debugreg(reg, val) do {                       \
> --- a/xen/include/asm-x86/msr-index.h
> +++ b/xen/include/asm-x86/msr-index.h
> @@ -79,6 +79,7 @@
>  #define IA32_DEBUGCTLMSR_BTINT		(1<<8) /* Branch Trace Interrupt */
>  #define IA32_DEBUGCTLMSR_BTS_OFF_OS	(1<<9)  /* BTS off if CPL 0 */
>  #define IA32_DEBUGCTLMSR_BTS_OFF_USR	(1<<10) /* BTS off if CPL > 0 */
> +#define IA32_DEBUGCTLMSR_RTM		(1<<15) /* RTM debugging enable */
>  
>  #define MSR_IA32_LASTBRANCHFROMIP	0x000001db
>  #define MSR_IA32_LASTBRANCHTOIP		0x000001dc
>
>
>
>
>
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> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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