Re: [Xen-devel] [PATCH v25 11/15] VPMU/AMD: Check MSR values before writing to hardware

[Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>]

On 6/19/2015 1:44 PM, Boris Ostrovsky wrote:
> A number of fields of PMU control MSRs are defined as Reserved. AMD
> documentation requires that such fields are preserved when the register
> is written by software.
>
> Add checks to amd_vpmu_do_wrmsr() to make sure that guests don't attempt
> to modify those bits.
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Reviewed-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@xxxxxxx>


> ---
>   xen/arch/x86/hvm/svm/vpmu.c | 49 +++++++++++++++++++++++++++++++++++++++------
>   1 file changed, 43 insertions(+), 6 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/svm/vpmu.c b/xen/arch/x86/hvm/svm/vpmu.c
> index 74d03a5..934f1b7 100644
> --- a/xen/arch/x86/hvm/svm/vpmu.c
> +++ b/xen/arch/x86/hvm/svm/vpmu.c
> @@ -48,6 +48,7 @@ static bool_t __read_mostly k7_counters_mirrored;
>   
>   #define F10H_NUM_COUNTERS   4
>   #define F15H_NUM_COUNTERS   6
> +#define MAX_NUM_COUNTERS    F15H_NUM_COUNTERS
>   
>   /* PMU Counter MSRs. */
>   static const u32 AMD_F10H_COUNTERS[] = {
> @@ -83,6 +84,11 @@ static const u32 AMD_F15H_CTRLS[] = {
>       MSR_AMD_FAM15H_EVNTSEL5
>   };
>   
> +/* Bits [63:42], [39:36], 21 and 19 are reserved */
> +#define CTRL_RSVD_MASK ((-1ULL & (~((1ULL << 42) - 1))) | \
> +                        (0xfULL << 36) | (1ULL << 21) | (1ULL << 19))
> +static uint64_t __read_mostly ctrl_rsvd[MAX_NUM_COUNTERS];
> +
>   /* Use private context as a flag for MSR bitmap */
>   #define msr_bitmap_on(vpmu)    do {                                    \
>                                      (vpmu)->priv_context = (void *)-1L; \
> @@ -92,17 +98,24 @@ static const u32 AMD_F15H_CTRLS[] = {
>                                  } while (0)
>   #define is_msr_bitmap_on(vpmu) ((vpmu)->priv_context != NULL)
>   
> -static inline int get_pmu_reg_type(u32 addr)
> +static inline int get_pmu_reg_type(u32 addr, unsigned int *idx)
>   {
>       if ( (addr >= MSR_K7_EVNTSEL0) && (addr <= MSR_K7_EVNTSEL3) )
> +    {
> +        *idx = addr - MSR_K7_EVNTSEL0;
>           return MSR_TYPE_CTRL;
> +    }
>   
>       if ( (addr >= MSR_K7_PERFCTR0) && (addr <= MSR_K7_PERFCTR3) )
> +    {
> +        *idx = addr - MSR_K7_PERFCTR0;
>           return MSR_TYPE_COUNTER;
> +    }
>   
>       if ( (addr >= MSR_AMD_FAM15H_EVNTSEL0) &&
>            (addr <= MSR_AMD_FAM15H_PERFCTR5 ) )
>       {
> +        *idx = (addr - MSR_AMD_FAM15H_EVNTSEL0) >> 1;
>           if (addr & 1)
>               return MSR_TYPE_COUNTER;
>           else
> @@ -140,6 +153,16 @@ static inline u32 get_fam15h_addr(u32 addr)
>       return addr;
>   }
>   
> +static void amd_vpmu_init_regs(struct xen_pmu_amd_ctxt *ctxt)
> +{
> +    unsigned i;
> +    uint64_t *ctrl_regs = vpmu_reg_pointer(ctxt, ctrls);
> +
> +    memset(&ctxt->regs[0], 0, 2 * sizeof(uint64_t) * num_counters);
> +    for ( i = 0; i < num_counters; i++ )
> +        ctrl_regs[i] = ctrl_rsvd[i];
> +}
> +
>   static void amd_vpmu_set_msr_bitmap(struct vcpu *v)
>   {
>       unsigned int i;
> @@ -289,19 +312,24 @@ static int amd_vpmu_do_wrmsr(unsigned int msr, uint64_t 
> msr_content,
>   {
>       struct vcpu *v = current;
>       struct vpmu_struct *vpmu = vcpu_vpmu(v);
> +    unsigned int idx = 0;
> +    int type = get_pmu_reg_type(msr, &idx);
>   
>       ASSERT(!supported);
>   
> +    if ( (type == MSR_TYPE_CTRL ) &&
> +         ((msr_content & CTRL_RSVD_MASK) != ctrl_rsvd[idx]) )
> +        return -EINVAL;
> +
>       /* For all counters, enable guest only mode for HVM guest */
> -    if ( has_hvm_container_vcpu(v) &&
> -         (get_pmu_reg_type(msr) == MSR_TYPE_CTRL) &&
> +    if ( has_hvm_container_vcpu(v) && (type == MSR_TYPE_CTRL) &&
>            !is_guest_mode(msr_content) )
>       {
>           set_guest_mode(msr_content);
>       }
>   
>       /* check if the first counter is enabled */
> -    if ( (get_pmu_reg_type(msr) == MSR_TYPE_CTRL) &&
> +    if ( (type == MSR_TYPE_CTRL) &&
>           is_pmu_enabled(msr_content) && !vpmu_is_set(vpmu, VPMU_RUNNING) )
>       {
>           if ( !acquire_pmu_ownership(PMU_OWNER_HVM) )
> @@ -313,7 +341,7 @@ static int amd_vpmu_do_wrmsr(unsigned int msr, uint64_t 
> msr_content,
>       }
>   
>       /* stop saving & restore if guest stops first counter */
> -    if ( (get_pmu_reg_type(msr) == MSR_TYPE_CTRL) &&
> +    if ( (type == MSR_TYPE_CTRL) &&
>           (is_pmu_enabled(msr_content) == 0) && vpmu_is_set(vpmu, VPMU_RUNNING) 
> )
>       {
>           vpmu_reset(vpmu, VPMU_RUNNING);
> @@ -433,7 +461,7 @@ int svm_vpmu_initialise(struct vcpu *v)
>       if ( !counters )
>           return -EINVAL;
>   
> -    ctxt = xzalloc_bytes(sizeof(*ctxt) +
> +    ctxt = xmalloc_bytes(sizeof(*ctxt) +
>                            2 * sizeof(uint64_t) * num_counters);
>       if ( !ctxt )
>       {
> @@ -445,6 +473,7 @@ int svm_vpmu_initialise(struct vcpu *v)
>   
>       ctxt->counters = sizeof(*ctxt);
>       ctxt->ctrls = ctxt->counters + sizeof(uint64_t) * num_counters;
> +    amd_vpmu_init_regs(ctxt);
>   
>       vpmu->context = ctxt;
>       vpmu->priv_context = NULL;
> @@ -457,6 +486,8 @@ int svm_vpmu_initialise(struct vcpu *v)
>   
>   int __init amd_vpmu_init(void)
>   {
> +    unsigned int i;
> +
>       switch ( current_cpu_data.x86 )
>       {
>       case 0x15:
> @@ -490,6 +521,12 @@ int __init amd_vpmu_init(void)
>           return -ENOSPC;
>       }
>   
> +    for ( i = 0; i < num_counters; i++ )
> +    {
> +        rdmsrl(ctrls[i], ctrl_rsvd[i]);
> +        ctrl_rsvd[i] &= CTRL_RSVD_MASK;
> +    }
> +
>       return 0;
>   }
>   

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