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

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2015/6/13 0:39, Wei Liu wrote:
> 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?
This was left to handle something inside modules_init(). But I think 
this change can be removed now.
> >       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.
Sure, so what about this?

/*
 * We really can't presume how many entries we can get in advance.
 */
if (*nr_entries)
    *nr_entries = 0;

> > +    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.
Okay, just let me try firstly.

Thanks
Tiejun

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