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.

Signed-off-by: Jim Fehlig <jfehlig(a)suse.com&gt; --- src/libxl/libxl_domain.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c index a5314b0..ed73cd2 100644 --- a/src/libxl/libxl_domain.c +++ b/src/libxl/libxl_domain.c @@ -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;

I saw this mail but didn't realise it required my input, sorry.

On Wed, Feb 01, 2017 at 04:00:54PM -0700, Jim Fehlig wrote: > Jim Fehlig wrote: >> 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. > > Any comments on this patch? xen-devel is already in cc, but I'll add Wei (one of > the Xen tools maintainers) and Juergen (author of commit 57f8b13c) for some > additional exposure :-). > > Currently, "out-of-the-box" Xen >= 4.8 + libvirt setup (dom0 autoballooning > enabled) is broken without this fix. > > Regards, > Jim > >> >> Signed-off-by: Jim Fehlig <jfehlig(a)suse.com&gt; >> --- >> src/libxl/libxl_domain.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c >> index a5314b0..ed73cd2 100644 >> --- a/src/libxl/libxl_domain.c >> +++ b/src/libxl/libxl_domain.c >> @@ -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, This should do the trick.