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libxl: fix dom0 autoballooning with Xen 4.8

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xen.git commit 57f8b13c changed several of the libxl memory
get/set functions to take 64 bit parameters. The libvirt
libxl driver still uses uint32_t variables for these various
parameters, which is particularly problematic for the
libxl_set_memory_target() function.

When dom0 autoballooning is enabled, libvirt (like xl) determines
the memory needed to start a domain and the memory available. If
memory available is less than memory needed, dom0 is ballooned
down by passing a negative value to libxl_set_memory_target()
'target_memkb' parameter. Prior to xen.git commit 57f8b13c,
'target_memkb' was an int32_t. Subtracting a larger uint32 from
a smaller uint32 and assigning it to int32 resulted in a negative
number. After commit 57f8b13c, the same subtraction is widened
to a int64, resulting in a large positive number. The simple
fix taken by this patch is to assign the difference of the
uint32 values to a temporary int32 variable, which is then
passed to 'target_memkb' parameter of libxl_set_memory_target().

Note that it is undesirable to change libvirt to use 64 bit
variables since it requires setting LIBXL_API_VERSION to 0x040800.
Currently libvirt supports LIBXL_API_VERSION >= 0x040400,
essentially Xen >= 4.4.
This commit is contained in:
Jim Fehlig 2017-01-17 15:11:32 -07:00
parent 5550dde150
commit f86a7a8372
1 changed files with 3 additions and 1 deletions
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4
src/libxl/libxl_domain.c
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@ -909,6 +909,7 @@ libxlDomainFreeMem(libxl_ctx *ctx, libxl_domain_config *d_config)
{
uint32_t needed_mem;
uint32_t free_mem;
int32_t target_mem;
int tries = 3;
int wait_secs = 10;
@ -922,7 +923,8 @@ libxlDomainFreeMem(libxl_ctx *ctx, libxl_domain_config *d_config)
if (free_mem >= needed_mem)
return 0;
if (libxl_set_memory_target(ctx, 0, free_mem - needed_mem,
target_mem = free_mem - needed_mem;
if (libxl_set_memory_target(ctx, 0, target_mem,
/* relative */ 1, 0) < 0)
goto error;