Re: [Xen-devel] [v3][PATCH 13/16] tools/libxl: detect and avoid conflicts with RDM

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Jun 11, 2015 at 09:15:22AM +0800, Tiejun Chen wrote:
[...]
> +++ b/tools/libxc/xc_hvm_build_x86.c
> @@ -21,6 +21,7 @@
>  #include <stdlib.h>
>  #include <unistd.h>
>  #include <zlib.h>
> +#include <assert.h>
>  
>  #include "xg_private.h"
>  #include "xc_private.h"
> @@ -270,7 +271,7 @@ static int setup_guest(xc_interface *xch,
>  
>      elf_parse_binary(&elf);
>      v_start = 0;
> -    v_end = args->mem_size;
> +    v_end = args->lowmem_end;

Why is this needed?
>  
>      if ( nr_pages > target_pages )
>          memflags |= XENMEMF_populate_on_demand;
> @@ -754,6 +755,8 @@ int xc_hvm_build_target_mem(xc_interface *xch,
>      args.mem_size = (uint64_t)memsize << 20;
>      args.mem_target = (uint64_t)target << 20;
>      args.image_file_name = image_name;
[...]
>  
> +static struct xen_reserved_device_memory
> +*xc_device_get_rdm(libxl__gc *gc,
> +                   uint32_t flag,
> +                   uint16_t seg,
> +                   uint8_t bus,
> +                   uint8_t devfn,
> +                   unsigned int *nr_entries)
> +{
> +    struct xen_reserved_device_memory *xrdm;
> +    int rc;
> +
> +    rc = xc_reserved_device_memory_map(CTX->xch, flag, seg, bus, devfn,
> +                                       NULL, nr_entries);

xc_reserved_device_memory_map dereferences nr_entries. You need to make
sure there is no garbage value in nr_entries. I.e. you need to
initialise nr_entries to 0 before passing it in.

> +    assert(rc <= 0);
> +    /* "0" means we have no any rdm entry. */
> +    if (!rc)
> +        goto out;
> +
> +    if (errno == ENOBUFS) {
> +        xrdm = malloc(*nr_entries * sizeof(xen_reserved_device_memory_t));
> +        if (!xrdm) {
> +            LOG(ERROR, "Could not allocate RDM buffer!\n");
> +            goto out;
> +        }
> +        rc = xc_reserved_device_memory_map(CTX->xch, flag, seg, bus, devfn,
> +                                           xrdm, nr_entries);
> +        if (rc) {
> +            LOG(ERROR, "Could not get reserved device memory maps.\n");
> +            *nr_entries = 0;
> +            free(xrdm);
> +            xrdm = NULL;
> +        }
> +    } else
> +        LOG(ERROR, "Could not get reserved device memory maps.\n");
> +
> + out:
> +    return xrdm;
> +}
> +
> +/*
> + * Check whether there exists rdm hole in the specified memory range.
> + * Returns true if exists, else returns false.
> + */
> +static bool overlaps_rdm(uint64_t start, uint64_t memsize,
> +                         uint64_t rdm_start, uint64_t rdm_size)
> +{
> +    return (start + memsize > rdm_start) && (start < rdm_start + rdm_size);
> +}
> +
> +/*
> + * Check reported RDM regions and handle potential gfn conflicts according
> + * to user preferred policy.
> + *
> + * RMRR can reside in address space beyond 4G theoretically, but we never
> + * see this in real world. So in order to avoid breaking highmem layout
> + * we don't solve highmem conflict. Note this means highmem rmrr could still
> + * be supported if no conflict.
> + *
> + * But in the case of lowmem, RMRR probably scatter the whole RAM space.
> + * Especially multiple RMRR entries would worsen this to lead a complicated
> + * memory layout. And then its hard to extend hvm_info_table{} to work
> + * hvmloader out. So here we're trying to figure out a simple solution to
> + * avoid breaking existing layout. So when a conflict occurs,
> + *
> + * #1. Above a predefined boundary (default 2G)
> + * - Move lowmem_end below reserved region to solve conflict;
> + *
> + * #2. Below a predefined boundary (default 2G)
> + * - Check strict/relaxed policy.
> + * "strict" policy leads to fail libxl. Note when both policies
> + * are specified on a given region, 'strict' is always preferred.
> + * "relaxed" policy issue a warning message and also mask this entry
> + * INVALID to indicate we shouldn't expose this entry to hvmloader.
> + */

This looks sensible. Thanks.

> diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
> index 4364ba4..85d74fd 100644
> --- a/tools/libxl/xl_cmdimpl.c
> +++ b/tools/libxl/xl_cmdimpl.c
> @@ -1374,6 +1374,9 @@ static void parse_config_data(const char *config_source,
>      if (!xlu_cfg_get_long (config, "videoram", &l, 0))
>          b_info->video_memkb = l * 1024;
>  
> +    if (!xlu_cfg_get_long (config, "rdm_mem_boundary", &l, 0))
> +        b_info->rdm_mem_boundary_memkb = l * 1024;
> +

Maybe you need to rearrange this patch series a bit more. The toolstack
side patches have mixed libxc, libxl and xl changes which is a bit hard
for me to tell what is needed by what. We can discuss this if you have
questions.

Wei.

>      if (!xlu_cfg_get_long(config, "max_event_channels", &l, 0))
>          b_info->event_channels = l;
>  
> -- 
> 1.9.1

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