Re: [Xen-devel] [PATCH v4 3/3] x86/hyperv: L0 assisted TLB flush

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, Feb 19, 2020 at 11:44:11AM +0000, Wei Liu wrote:
> Implement L0 assisted TLB flush for Xen on Hyper-V. It takes advantage
> of several hypercalls:
> 
>  * HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST
>  * HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX
>  * HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE
>  * HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX
> 
> Pick the most efficient hypercalls available.
> 
> Signed-off-by: Wei Liu <liuwe@microsoft.com>

LGTM:

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

> +int cpumask_to_vpset(struct hv_vpset *vpset,
> +                     const cpumask_t *mask)
> +{
> +    int nr = 1;
> +    unsigned int cpu, vcpu_bank, vcpu_offset;
> +    unsigned int max_banks = ms_hyperv.max_vp_index / 64;
> +
> +    /* Up to 64 banks can be represented by valid_bank_mask */
> +    if ( max_banks > 64 )
> +        return -E2BIG;
> +
> +    /* Clear all banks to avoid flushing unwanted CPUs */
> +    for ( vcpu_bank = 0; vcpu_bank < max_banks; vcpu_bank++ )
> +        vpset->bank_contents[vcpu_bank] = 0;
> +
> +    vpset->format = HV_GENERIC_SET_SPARSE_4K;
> +
> +    for_each_cpu ( cpu, mask )
> +    {
> +        unsigned int vcpu = hv_vp_index(cpu);
> +
> +        vcpu_bank = vcpu / 64;
> +        vcpu_offset = vcpu % 64;
> +
> +        __set_bit(vcpu_offset, &vpset->bank_contents[vcpu_bank]);
> +
> +        if ( vcpu_bank >= nr )
> +            nr = vcpu_bank + 1;
> +    }
> +
> +    /* Some banks may be empty but that's ok */
> +    vpset->valid_bank_mask = ~0ULL >> (64 - nr);

You could also use the recently introduced bitmap_set here.

Thanks, Roger.

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