Re: [PATCH V2 3/3] libxl/arm: Add handling of extended regions for DomU

[Oleksandr]

Hi Stefano

[snip]






+static void finalise_ext_region(libxl__gc *gc, struct xc_dom_image 
*dom)
+{
+    void *fdt = dom->devicetree_blob;
+    uint32_t regs[(GUEST_ROOT_ADDRESS_CELLS + 
GUEST_ROOT_SIZE_CELLS) * 2];
+    be32 *cells = &regs[0];
+    uint64_t region_size = 0, region_base, bank1end_align, 
bank1end_max;
+    uint32_t gpaddr_bits;
+    libxl_physinfo info;
+    int offset, rc;
+
+    offset = fdt_path_offset(fdt, "/hypervisor");
+    assert(offset > 0);
+
+    if (strcmp(dom->guest_type, "xen-3.0-aarch64")) {
+        LOG(WARN, "The extended region is only supported for 64-bit 
guest");
+        goto out;
+    }
+
+    rc = libxl_get_physinfo(CTX, &info);
+    assert(!rc);
+
+    gpaddr_bits = info.gpaddr_bits;
+    assert(gpaddr_bits >= 32 && gpaddr_bits <= 48);
+
+    /*
+     * Try to allocate single 1GB-aligned extended region from the 
second RAM
+     * bank (above 4GB) taking into the account the maximum 
supported guest
+     * address space size and the amount of memory assigned to the 
guest.
+     * The maximum size of the region is 128GB.
+     */
+    bank1end_max = min(1ULL << gpaddr_bits, GUEST_RAM1_BASE + 
GUEST_RAM1_SIZE);
+    bank1end_align = GUEST_RAM1_BASE +
+        ALIGN_UP_TO_GB((uint64_t)dom->rambank_size[1] << 
XC_PAGE_SHIFT);
+
+    if (bank1end_max <= bank1end_align) {
+        LOG(WARN, "The extended region cannot be allocated, not 
enough space");
+        goto out;
+    }
+
+    if (bank1end_max - bank1end_align > EXT_REGION_SIZE) {
+        region_base = bank1end_max - EXT_REGION_SIZE;
+        region_size = EXT_REGION_SIZE;
+    } else {
+        region_base = bank1end_align;
+        region_size = bank1end_max - bank1end_align;
+    }
+
+out:
+    /*
+     * The first region for grant table space must be always present.
+     * If we managed to allocate the extended region then insert it as
+     * a second region.
+     * TODO If we failed to allocate the region, we end up inserting
+     * zero-sized region. This is because we don't know in advance 
when
+     * creating hypervisor node whether it would be possible to 
allocate
+     * a region, but we have to create a placeholder anyway. The 
Linux driver
+     * is able to deal with by checking the region size. We cannot 
choose
+     * a region when creating hypervisor node because the guest 
memory layout
+     * is not know at that moment (and dom->rambank_size[1] is empty).
+     * We need to find a way not to expose invalid regions.
+     */
This is not great -- it would be barely spec compliant.

Absolutely agree.



When make_hypervisor_node is called we know the max memory of the guest
as build_info.max_memkb should be populate, right?

Right. Just a small change to pass build_info to 
make_hypervisor_node() is needed.



If so, we could at least detect whether we can have an extended region
(if not caculate the exact start address) from make_hypervisor_node.

total_guest_memory = build_info.max_memkb * 1024;
rambank1_approx = total_guest_memory - GUEST_RAM0_SIZE;
extended_region_size = GUEST_RAM1_SIZE - rambank1_approx;

if (extended_region_size >= MIN_EXT_REGION_SIZE)
     allocate_ext_region
Good point! I will recheck that. I would prefer avoid spreading 
extended region handling (introduce finalise_ext_region())
and do everything from the make_hypervisor_node().
I experimented with that, so we can indeed calculate the address and 
size of extended region from make_hypervisor_node(),
there is no need for finalise_ext_region(). So, there won't be any 
zero-sized region anymore (due to unpopulated placeholder) if we fail to 
allocate extended region.
Thanks for the idea!

[snip]


--
Regards,

Oleksandr Tyshchenko