Re: [PATCH 08/12] xen/arm: if is_domain_direct_mapped use native addresses for GICv2

[Julien Grall <julien@xen.org>]

On 01/05/2020 02:26, Stefano Stabellini wrote:
> On Wed, 15 Apr 2020, Julien Grall wrote:
>> On 15/04/2020 02:02, Stefano Stabellini wrote:
>>> Today we use native addresses to map the GICv2 for Dom0 and fixed
>>> addresses for DomUs.
>>>
>>> This patch changes the behavior so that native addresses are used for
>>> any domain that is_domain_direct_mapped.
>>>
>>> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
>>> ---
>>>    xen/arch/arm/domain_build.c | 10 +++++++---
>>>    xen/arch/arm/vgic-v2.c      | 12 ++++++------
>>>    xen/arch/arm/vgic/vgic-v2.c |  2 +-
>>>    xen/include/asm-arm/vgic.h  |  1 +
>>>    4 files changed, 15 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
>>> index 627e0c5e8e..303bee60f6 100644
>>> --- a/xen/arch/arm/domain_build.c
>>> +++ b/xen/arch/arm/domain_build.c
>>> @@ -1643,8 +1643,12 @@ static int __init make_gicv2_domU_node(struct
>>> kernel_info *kinfo)
>>>        int res = 0;
>>>        __be32 reg[(GUEST_ROOT_ADDRESS_CELLS + GUEST_ROOT_SIZE_CELLS) * 2];
>>>        __be32 *cells;
>>> +    struct domain *d = kinfo->d;
>>> +    char buf[38];
>>>    -    res = fdt_begin_node(fdt,
>>> "interrupt-controller@"__stringify(GUEST_GICD_BASE));
>>> +    snprintf(buf, sizeof(buf), "interrupt-controller@%"PRIx64,
>>> +             d->arch.vgic.dbase);
>>> +    res = fdt_begin_node(fdt, buf);
>>>        if ( res )
>>>            return res;
>>>    @@ -1666,9 +1670,9 @@ static int __init make_gicv2_domU_node(struct
>>> kernel_info *kinfo)
>>>          cells = &reg[0];
>>>        dt_child_set_range(&cells, GUEST_ROOT_ADDRESS_CELLS,
>>> GUEST_ROOT_SIZE_CELLS,
>>> -                       GUEST_GICD_BASE, GUEST_GICD_SIZE);
>>> +                       d->arch.vgic.dbase, GUEST_GICD_SIZE);
>>>        dt_child_set_range(&cells, GUEST_ROOT_ADDRESS_CELLS,
>>> GUEST_ROOT_SIZE_CELLS,
>>> -                       GUEST_GICC_BASE, GUEST_GICC_SIZE);
>>> +                       d->arch.vgic.cbase, GUEST_GICC_SIZE);
>>
>> You can't use the native base address and not the native size. Particularly,
>> this is going to screw any GIC using 8KB alias.
> 
> I don't follow why it could cause problems with a GIC using the 8KB
> alias. Maybe an example (even a fake example) would help.

The GICC interface is composed of the two 4KB pages. In some of the 
implementation, each pages starts at a 64KB aligned address. Each page 
are also aliased every 4KB in the 64KB region.

For guest, we don't expose the full 128KB region but only part of it 
(8KB). So the guest interface is the same regardless the underlying 
implementation of the GIC.

vgic.cbase points to the beginning of the first region. So what you are 
mapping is the first 8KB of the first region. The second region is not 
mapped at all.

As the pages are aliased, the trick we use is to map from vgic.cbase + 
60KB (vgic_v2.hw.aliased_offset). This means the 2 pages will now be 
contiguous in the guest physical memory.

>> It would be preferable if only expose part of the CPU interface as we do for
>> the guest. So d->arch.vgic.cbase would be equal to vgic_v2_hw.dbase +

I meant cbase rather than dbase here.

>> vgic_v2.hw.aliased_offset.
> 

Cheers,

-- 
Julien Grall