Re: [PATCH V6 2/2] libxl/arm: Add handling of extended regions for DomU

[Julien Grall <julien@xxxxxxx>]

Hi Oleksandr,

On 13/10/2021 16:49, Oleksandr wrote:
> On 13.10.21 18:15, Julien Grall wrote:
> > On 13/10/2021 14:46, Oleksandr wrote:
> > > Hi Julien
> > Hi Oleksandr,
> Hi Julien
>
>
> Thank you for the prompt response.
>
>
> > > On 13.10.21 00:43, Oleksandr wrote:
> > > diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
> > > index e3140a6..53ae0f3 100644
> > > --- a/tools/libs/light/libxl_arm.c
> > > +++ b/tools/libs/light/libxl_arm.c
> > > @@ -615,9 +615,12 @@ static int make_hypervisor_node(libxl__gc *gc, 
> > > void *fdt,
> > >                                 "xen,xen");
> > >       if (res) return res;
> > >
> > > -    /* reg 0 is grant table space */
> > > +    /*
> > > +     * reg 0 is a placeholder for grant table space, reg 1...N are
> > > +     * the placeholders for extended regions.
> > > +     */
> > >       res = fdt_property_regs(gc, fdt, GUEST_ROOT_ADDRESS_CELLS, 
> > > GUEST_ROOT_SIZE_CELLS,
> > > -                            1,GUEST_GNTTAB_BASE, GUEST_GNTTAB_SIZE);
> > > +                            GUEST_RAM_BANKS + 1, 0, 0, 0, 0, 0, 0);
> > Here you are relying on GUEST_RAM_BANKS == 2. I think this is pretty 
> > fragile as this may change in the future.
> > fdt_property_regs() is not really suitable for here. I would suggest 
> > to create a new helper fdt_property_placeholder() which takes the 
> > address cells, size cells and the number of ranges. The function will 
> > then create N range that are zeroed.
> You are right. Probably, we could add an assert here for now to be 
> triggered if "GUEST_RAM_BANKS != 2"?
> But, if you still think we need to make it with the helper right now, I 
> will. However, I don't know how long this will take.
I would prefer if we introduce the helper now. Below a potential version 
(not compiled):
diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
index e3140a6e0039..df59a0521412 100644
--- a/tools/libs/light/libxl_arm.c
+++ b/tools/libs/light/libxl_arm.c
@@ -269,6 +269,20 @@ static int fdt_property_regs(libxl__gc *gc, void *fdt,
     return fdt_property(fdt, "reg", regs, sizeof(regs));
 }

+static int fdt_property_reg_placeholder(libxl__gc *gc, void *fdt,
+                                        unsigned int addr_cells,
+                                        unsigned int size_cells,
+                                        unsigned int num_regs)
+{
+    uint32_t regs[num_regs * (addr_cells + size_cells)];
+
+    for (i = 0 ; i < num_regs; i++) {
+        set_range(&cells, addr_cells, size_cells, 0, 0);
+    }
+
+    return fdt_property(fdt, "reg", regs, sizeof(regs));
+}
+
 static int make_root_properties(libxl__gc *gc,
                                 const libxl_version_info *vers,

> > > +{
> > > +    void *fdt = dom->devicetree_blob;
> > > +    uint64_t region_size[GUEST_RAM_BANKS] = {0}, 
> > > region_base[GUEST_RAM_BANKS],
> > > +        bankend[GUEST_RAM_BANKS];
> > > +    uint32_t regs[(GUEST_ROOT_ADDRESS_CELLS + GUEST_ROOT_SIZE_CELLS) *
> > > +                  (GUEST_RAM_BANKS + 1)];
> > > +    be32 *cells = &regs[0];
> > > +    const uint64_t bankbase[] = GUEST_RAM_BANK_BASES;
> > > +    const uint64_t banksize[] = GUEST_RAM_BANK_SIZES;
> > > +    unsigned int i, len, nr_regions = 0;
> > > +    libxl_dominfo info;
> > > +    int offset, rc;
> > > +
> > > +    offset = fdt_path_offset(fdt, "/hypervisor");
> > > +    assert(offset > 0);
> > > +
> > > +    rc = libxl_domain_info(CTX, &info, dom->guest_domid);
> > > +    assert(!rc);
> > > +
> > > +    assert(info.gpaddr_bits <= 64);
> > Neither of the two should be assert(). They should be proper check so 
> > we don't end up with a disaster (in particularly for the former) if 
> > there is a problem.
> I looked at the similar finalise_*(), and it looks like no one bothers 
> with returning an error. Of course, this is not an excuse, will add a 
> proper check.
This is a bit unfortunate. I would prefer if this can be avoided for new 
code (the more libxl__arch_domain_finalise_hw_description() can already 
propagate the error).
Cheers,

--
Julien Grall