Re: [PATCH] x86/hvm: allow for more fine grained assisted flush

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Apr 30, 2020 at 11:17:25AM +0200, Roger Pau Monne wrote:
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 814b7020d8..1d41b6e2ea 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -4011,17 +4011,42 @@ static void hvm_s3_resume(struct domain *d)
>      }
>  }
>  
> -static bool always_flush(void *ctxt, struct vcpu *v)
> +static bool flush_check(void *mask, struct vcpu *v)
>  {
> -    return true;
> +    return mask ? test_bit(v->vcpu_id, (unsigned long *)mask) : true;
>  }
>  
> -static int hvmop_flush_tlb_all(void)
> +static int hvmop_flush_tlb(XEN_GUEST_HANDLE_PARAM(xen_hvm_flush_tlbs_t) uop)
>  {
> +    xen_hvm_flush_tlbs_t op;
> +    DECLARE_BITMAP(mask, HVM_MAX_VCPUS) = { };
> +    bool valid_mask = false;
> +
>      if ( !is_hvm_domain(current->domain) )
>          return -EINVAL;
>  
> -    return paging_flush_tlb(always_flush, NULL) ? 0 : -ERESTART;
> +    if ( !guest_handle_is_null(uop) )
> +    {
> +        if ( copy_from_guest(&op, uop, 1) )
> +            return -EFAULT;
> +
> +        /*
> +         * TODO: implement support for the other features present in
> +         * xen_hvm_flush_tlbs_t: flushing a specific virtual address and not
> +         * flushing global mappings.
> +         */
> +
> +        if ( op.mask_size > ARRAY_SIZE(mask) )

This should also check that the passed in flags are correct, ie:

if ( op.mask_size > ARRAY_SIZE(mask) ||
     (op.flags & ~(HVMOP_flush_global | HVMOP_flush_va_valid)) )
     return -EINVAL;

Roger.