Re: [PATCH v8 5/8] hw/misc/riscv_iopmp: Add API to set up IOPMP protection for system memory

[Ethan Chen via <qemu-devel@nongnu.org>]

On Thu, Aug 08, 2024 at 02:23:56PM +1000, Alistair Francis wrote:
> 
> On Mon, Jul 15, 2024 at 8:13 PM Ethan Chen via <qemu-devel@nongnu.org> wrote:
> >
> > To enable system memory transactions through the IOPMP, memory regions must
> > be moved to the IOPMP downstream and then replaced with IOMMUs for IOPMP
> > translation.
> >
> > The iopmp_setup_system_memory() function copies subregions of system memory
> > to create the IOPMP downstream and then replaces the specified memory
> > regions in system memory with the IOMMU regions of the IOPMP. It also
> > adds entries to a protection map that records the relationship between
> > physical address regions and the IOPMP, which is used by the IOPMP DMA
> > API to send transaction information.
> >
> > Signed-off-by: Ethan Chen <ethan84@andestech.com>
> > ---
> >  hw/misc/riscv_iopmp.c         | 61 +++++++++++++++++++++++++++++++++++
> >  include/hw/misc/riscv_iopmp.h |  3 ++
> >  2 files changed, 64 insertions(+)
> >
> > diff --git a/hw/misc/riscv_iopmp.c b/hw/misc/riscv_iopmp.c
> > index db43e3c73f..e62ac57437 100644
> > --- a/hw/misc/riscv_iopmp.c
> > +++ b/hw/misc/riscv_iopmp.c
> > @@ -1151,4 +1151,65 @@ iopmp_register_types(void)
> >      type_register_static(&iopmp_iommu_memory_region_info);
> >  }
> >
> > +/*
> > + * Copies subregions from the source memory region to the destination memory
> > + * region
> > + */
> > +static void copy_memory_subregions(MemoryRegion *src_mr, MemoryRegion *dst_mr)
> > +{
> > +    int32_t priority;
> > +    hwaddr addr;
> > +    MemoryRegion *alias, *subregion;
> > +    QTAILQ_FOREACH(subregion, &src_mr->subregions, subregions_link) {
> > +        priority = subregion->priority;
> > +        addr = subregion->addr;
> > +        alias = g_malloc0(sizeof(MemoryRegion));
> > +        memory_region_init_alias(alias, NULL, subregion->name, subregion, 0,
> > +                                 memory_region_size(subregion));
> > +        memory_region_add_subregion_overlap(dst_mr, addr, alias, priority);
> > +    }
> > +}
> 
> This seems strange. Do we really need to do this?
> 
> I haven't looked at the memory_region stuff for awhile, but this seems
> clunky and prone to breakage.
> 
> We already link s->iommu with the system memory
>

s->iommu occupies the address of the protected devices in system
memory. Since IOPMP does not alter address, the target address space 
must differ from system memory to avoid infinite recursive iommu access.

The transaction will be redirected to a downstream memory region, which
is almost identical to system memory but without the iommu memory
region of IOPMP. 

This function serves as a helper to create that downstream memory region.

Thanks,
Ethan Chen

> Alistair
> 
> > +
> > +/*
> > + * Create downstream of system memory for IOPMP, and overlap memory region
> > + * specified in memmap with IOPMP translator. Make sure subregions are added to
> > + * system memory before call this function. It also add entry to
> > + * iopmp_protection_memmaps for recording the relationship between physical
> > + * address regions and IOPMP.
> > + */
> > +void iopmp_setup_system_memory(DeviceState *dev, const MemMapEntry *memmap,
> > +                               uint32_t map_entry_num)
> > +{
> > +    IopmpState *s = IOPMP(dev);
> > +    uint32_t i;
> > +    MemoryRegion *iommu_alias;
> > +    MemoryRegion *target_mr = get_system_memory();
> > +    MemoryRegion *downstream = g_malloc0(sizeof(MemoryRegion));
> > +    memory_region_init(downstream, NULL, "iopmp_downstream",
> > +                       memory_region_size(target_mr));
> > +    /* Copy subregions of target to downstream */
> > +    copy_memory_subregions(target_mr, downstream);
> > +
> > +    iopmp_protection_memmap *map;
> > +    for (i = 0; i < map_entry_num; i++) {
> > +        /* Memory access to protected regions of target are through IOPMP */
> > +        iommu_alias = g_new(MemoryRegion, 1);
> > +        memory_region_init_alias(iommu_alias, NULL, "iommu_alias",
> > +                                 MEMORY_REGION(&s->iommu), memmap[i].base,
> > +                                 memmap[i].size);
> > +        memory_region_add_subregion_overlap(target_mr, memmap[i].base,
> > +                                            iommu_alias, 1);
> > +        /* Record which IOPMP is responsible for the region */
> > +        map = g_new0(iopmp_protection_memmap, 1);
> > +        map->iopmp_s = s;
> > +        map->entry.base = memmap[i].base;
> > +        map->entry.size = memmap[i].size;
> > +        QLIST_INSERT_HEAD(&iopmp_protection_memmaps, map, list);
> > +    }
> > +    s->downstream = downstream;
> > +    address_space_init(&s->downstream_as, s->downstream,
> > +                       "iopmp-downstream-as");
> > +}
> > +
> > +
> >  type_init(iopmp_register_types);
> > diff --git a/include/hw/misc/riscv_iopmp.h b/include/hw/misc/riscv_iopmp.h
> > index b8fe479108..ebe9c4bc4a 100644
> > --- a/include/hw/misc/riscv_iopmp.h
> > +++ b/include/hw/misc/riscv_iopmp.h
> > @@ -165,4 +165,7 @@ typedef struct IopmpState {
> >      uint32_t fabricated_v;
> >  } IopmpState;
> >
> > +void iopmp_setup_system_memory(DeviceState *dev, const MemMapEntry *memmap,
> > +                               uint32_t mapentry_num);
> > +
> >  #endif
> > --
> > 2.34.1
> >
> >