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libxl: Fix Domain-0 ballooning logic

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When Domain-0 autoballooning is enabled, it's possible that memory may
need to be ballooned down in Domain-0 to accommodate the needs of another
virtual machine. libxlDomainFreeMemory handles this task, but due to a
logic bug is underflowing the variable containing Domain-0 new
target memory. The resulting huge numbers are filtered by
libxlSetMemoryTargetWrapper and memory is not changed.

Under the covers, libxlDomainFreeMemory uses Xen's libxl_set_memory_target
API, which includes a 'relative' parameter for specifying how to set the
target. If true, the target is an increment/decrement value over the
current memory, otherwise target is taken as an absolute value.
libxlDomainFreeMemory sets 'relative' to true, but never allows for
negative values by declaring the target memory variable as an unsigned.
Fix by declaring the variable as signed, which also requried adjusting
libxlSetMemoryTargetWrapper.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
Jim Fehlig 2023-09-18 09:59:39 -06:00
parent 4096a59e6e
commit 417197a38f
2 changed files with 7 additions and 11 deletions
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16
src/libxl/libxl_api_wrapper.h
View File

@ -193,24 +193,20 @@ libxlSendTriggerWrapper(libxl_ctx *ctx,
static inline int
libxlSetMemoryTargetWrapper(libxl_ctx *ctx,
uint32_t domid,
uint64_t target_memkb,
int64_t target_memkb,
int relative,
int enforce)
{
int ret = -1;
/* Technically this guard could be LIBXL_HAVE_MEMKB_64BITS */
#if LIBXL_API_VERSION < 0x040800
if (target_memkb < UINT_MAX) {
uint32_t val32 = target_memkb;
#ifdef LIBXL_HAVE_MEMKB_64BITS
ret = libxl_set_memory_target(ctx, domid, target_memkb, relative, enforce);
#else
if (target_memkb < INT_MAX) {
int32_t val32 = target_memkb;
ret = libxl_set_memory_target(ctx, domid, val32, relative, enforce);
}
#else
if (target_memkb < LLONG_MAX) {
int64_t val64 = target_memkb;
ret = libxl_set_memory_target(ctx, domid, val64, relative, enforce);
}
#endif
return ret;

2
src/libxl/libxl_domain.c
View File

@ -926,7 +926,7 @@ libxlDomainFreeMem(libxl_ctx *ctx, libxl_domain_config *d_config)
{
uint64_t needed_mem;
uint64_t free_mem;
uint64_t target_mem;
int64_t target_mem;
int tries = 3;
int wait_secs = 10;