Re: Can't boot guest with more than 3585MB when using large pages

Marcelo Tosatti
2009-04-03T23:29:30Z

On Tue, Mar 24, 2009 at 04:57:46PM -0500, Ryan Harper wrote:
> * Alex Williamson <alex.williamson@hp.com> [2009-03-24 16:07]:
> >
> > On a 2.6.29, x86_64 host/guest, what's special about specifying a guest
> > size of -m 3586 when using -mem-path backed by hugetlbfs? 3585 works,
> > 3586 hangs here:
> >
> > ...
> > PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
> > Placing 64MB software IO TLB between ffff880020000000 - ffff880024000000
> > software IO TLB at phys 0x20000000 - 0x24000000
> > Memory: 3504832k/4196352k available (2926k kernel code, 524740k absent, 166780k reserved, 1260k data, 496k init)
> >
> > I can back -mem-path by tmpfs or disk and it works fine. Also works
> > with no -mem-path, but it would obviously be nice to benefit from large
> > pages on big guests. The system has plenty of huge pages to back the
> > request, and booting with -mem-prealloc makes no difference. Tested on
> > latest git as of today. Thanks,
>
> I've seen this as well, haven't had a chance to dig into the issue yet
> either. Certainly can test patches if anyone has an idea of what's
> wrong here.

Can you please try the following

------

qemu: kvm: fixup 4GB+ memslot large page alignment

Need to align the 4GB+ memslot after we know its address, not before.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/qemu/hw/pc.c b/qemu/hw/pc.c
index d4a4320..cc84772 100644
--- a/qemu/hw/pc.c
+++ b/qemu/hw/pc.c
@@ -866,6 +866,7 @@ static void pc_init1(ram_addr_t ram_size, int vga_ram_size,

/* above 4giga memory allocation */
if (above_4g_mem_size > 0) {
+ ram_addr = qemu_ram_alloc(above_4g_mem_size);
if (hpagesize) {
if (ram_addr & (hpagesize-1)) {
unsigned long aligned_addr;
@@ -874,7 +875,6 @@ static void pc_init1(ram_addr_t ram_size, int vga_ram_size,
ram_addr = aligned_addr;
}
}
- ram_addr = qemu_ram_alloc(above_4g_mem_size);
cpu_register_physical_memory(0x100000000ULL,
above_4g_mem_size,
ram_addr);