Re: [PATCH v3 1/4] xen/domctl, tools: Introduce a new domctl to get guest memory map

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.04.2024 10:16, Henry Wang wrote:
> --- a/tools/libs/ctrl/xc_domain.c
> +++ b/tools/libs/ctrl/xc_domain.c
> @@ -697,6 +697,39 @@ int xc_domain_setmaxmem(xc_interface *xch,
>      return do_domctl(xch, &domctl);
>  }
>  
> +int xc_get_domain_mem_map(xc_interface *xch, uint32_t domid,
> +                          struct xen_mem_region mem_regions[],
> +                          uint32_t *nr_regions)
> +{
> +    int rc;
> +    struct xen_domctl domctl = {
> +        .cmd         = XEN_DOMCTL_get_mem_map,
> +        .domain      = domid,
> +        .u.mem_map = {
> +            .nr_mem_regions = *nr_regions,
> +            .pad            = 0,

This isn't needed: By there being an initializer for the struct, all
unmentioned fields will be set to 0 anyway.

> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -696,6 +696,7 @@ int arch_domain_create(struct domain *d,
>  {
>      unsigned int count = 0;
>      int rc;
> +    struct mem_map_domain *mem_map = &d->arch.mem_map;
>  
>      BUILD_BUG_ON(GUEST_MAX_VCPUS < MAX_VIRT_CPUS);
>  
> @@ -785,6 +786,20 @@ int arch_domain_create(struct domain *d,
>      d->arch.sve_vl = config->arch.sve_vl;
>  #endif
>  
> +    if ( mem_map->nr_mem_regions < XEN_MAX_MEM_REGIONS )
> +    {
> +        mem_map->regions[mem_map->nr_mem_regions].start = GUEST_MAGIC_BASE;
> +        mem_map->regions[mem_map->nr_mem_regions].size = GUEST_MAGIC_SIZE;
> +        mem_map->regions[mem_map->nr_mem_regions].type = 
> GUEST_MEM_REGION_MAGIC;
> +        mem_map->nr_mem_regions++;
> +    }
> +    else
> +    {
> +        printk("Exceed max number of supported memory map regions\n");

Debugging leftover?

> --- a/xen/arch/arm/domctl.c
> +++ b/xen/arch/arm/domctl.c
> @@ -148,7 +148,6 @@ long arch_do_domctl(struct xen_domctl *domctl, struct 
> domain *d,
>  
>          return 0;
>      }
> -
>      case XEN_DOMCTL_vuart_op:
>      {
>          int rc;

Why? Instead you want ...

> @@ -176,6 +175,37 @@ long arch_do_domctl(struct xen_domctl *domctl, struct 
> domain *d,
>  
>          return rc;
>      }
> +    case XEN_DOMCTL_get_mem_map:

... separating blank line above this line and ...

> +    {
> +        int rc = 0;
> +        uint32_t nr_regions, i;
> +
> +        if ( domctl->u.mem_map.pad )
> +            return -EINVAL;
> +
> +        /*
> +         * Cap the number of regions to the minimum value between toolstack 
> and
> +         * hypervisor to avoid overflowing the buffer.
> +         */
> +        nr_regions = min(d->arch.mem_map.nr_mem_regions,
> +                         domctl->u.mem_map.nr_mem_regions);
> +
> +        domctl->u.mem_map.nr_mem_regions = nr_regions;
> +
> +        for ( i = 0; i < nr_regions; i++ )
> +        {
> +            if ( d->arch.mem_map.regions[i].pad )
> +                return -EINVAL;
> +        }
> +
> +        if ( copy_to_guest(domctl->u.mem_map.buffer,
> +                           d->arch.mem_map.regions,
> +                           nr_regions) ||
> +             __copy_to_guest(u_domctl, domctl, 1) )
> +            rc = -EFAULT;
> +
> +        return rc;
> +    }
>      default:

... this one.

Further with the way you use min() above, how is the caller going to know
whether it simply specified too small an array?

And then you check d->arch.mem_map.regions[i].pad. Why's that? And even
if needed here for some reason, that's surely not EINVAL, but an internal
error in Xen.

Finally instead of __copy_to_guest() can't you use __copy_field_to_guest(),
for just nr_regions?

> --- a/xen/include/public/domctl.h
> +++ b/xen/include/public/domctl.h
> @@ -946,6 +946,31 @@ struct xen_domctl_paging_mempool {
>      uint64_aligned_t size; /* Size in bytes. */
>  };
>  
> +#ifndef XEN_MAX_MEM_REGIONS
> +#define XEN_MAX_MEM_REGIONS 1
> +#endif
> +
> +struct xen_mem_region {
> +    uint64_aligned_t start;
> +    uint64_aligned_t size;
> +    uint32_t         type;

What is this field set to? I see no #define(s) in this header. If it's
the GUEST_MEM_REGION_* in the Arm header, a connection needs to be made.
Also note that GUEST_MEM_REGION_* violate name space requirements: New
additions should have XEN_ / xen_ prefixes on their names.

> +    /* Must be zero */
> +    uint32_t         pad;

This, being OUT only, should not be required to be set by the caller. As
long as no use appears, Xen merely ought to guarantee that it'll be 0 upon
return.

Jan