RE: [PATCH V4 01/10] xen/arm: introduce domain on Static Allocation

[Penny Zheng <Penny.Zheng@arm.com>]

Hi Julien

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: Tuesday, August 17, 2021 1:28 AM
> To: Penny Zheng <Penny.Zheng@arm.com>; xen-devel@lists.xenproject.org;
> sstabellini@kernel.org
> Cc: Bertrand Marquis <Bertrand.Marquis@arm.com>; Wei Chen
> <Wei.Chen@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH V4 01/10] xen/arm: introduce domain on Static Allocation
> 
> 
> 
> On 16/08/2021 06:21, Penny Zheng wrote:
> > Hi Julien
> 
> Hi Penny,
> 
> >> -----Original Message-----
> >> From: Julien Grall <julien@xen.org>
> >> Sent: Wednesday, August 11, 2021 9:32 PM
> >> To: Penny Zheng <Penny.Zheng@arm.com>;
> >> xen-devel@lists.xenproject.org; sstabellini@kernel.org
> >> Cc: Bertrand Marquis <Bertrand.Marquis@arm.com>; Wei Chen
> >> <Wei.Chen@arm.com>; nd <nd@arm.com>
> >> Subject: Re: [PATCH V4 01/10] xen/arm: introduce domain on Static
> >> Allocation
> >>
> >> Hi Penny,
> >>
> >> On 28/07/2021 11:27, Penny Zheng wrote:
> >>> Static Allocation refers to system or sub-system(domains) for which
> >>> memory areas are pre-defined by configuration using physical address
> >> ranges.
> >>> Those pre-defined memory, -- Static Memory, as parts of RAM reserved
> >>> in the beginning, shall never go to heap allocator or boot allocator
> >>> for any
> >> use.
> >>>
> >>> Domains on Static Allocation is supported through device tree
> >>> property `xen,static-mem` specifying reserved RAM banks as this domain's
> guest RAM.
> >>> By default, they shall be mapped to the fixed guest RAM address
> >>> `GUEST_RAM0_BASE`, `GUEST_RAM1_BASE`.
> >>>
> >>> This patch introduces this new `xen,static-mem` feature, and also
> >>> documents and parses this new attribute at boot time and stores
> >>> related info in static_mem for later initialization.
> >>>
> >>> Signed-off-by: Penny Zheng <penny.zheng@arm.com>
> >>> ---
> >>>    docs/misc/arm/device-tree/booting.txt | 40 +++++++++++++++++++++
> >>>    xen/arch/arm/bootfdt.c                | 51 +++++++++++++++++++++++++++
> >>>    xen/include/asm-arm/setup.h           |  2 ++
> >>>    3 files changed, 93 insertions(+)
> >>>
> >>> diff --git a/docs/misc/arm/device-tree/booting.txt
> >>> b/docs/misc/arm/device-tree/booting.txt
> >>> index 5243bc7fd3..2a1ddca29b 100644
> >>> --- a/docs/misc/arm/device-tree/booting.txt
> >>> +++ b/docs/misc/arm/device-tree/booting.txt
> >>> @@ -268,3 +268,43 @@ The DTB fragment is loaded at 0xc000000 in the
> >> example above. It should
> >>>    follow the convention explained in docs/misc/arm/passthrough.txt. The
> >>>    DTB fragment will be added to the guest device tree, so that the guest
> >>>    kernel will be able to discover the device.
> >>> +
> >>> +
> >>> +Static Allocation
> >>> +=============
> >>> +
> >>> +Static Allocation refers to system or sub-system(domains) for which
> >>> +memory areas are pre-defined by configuration using physical
> >>> +address
> >> ranges.
> >>> +Those pre-defined memory, -- Static Memory, as parts of RAM
> >>> +reserved in the beginning, shall never go to heap allocator or boot
> >>> +allocator for any
> >> use.
> >>
> >> I don't understand "as parts of RAM reserved in the beginning". Could
> >> you clarify it?
> >>
> >
> > I mean, static memory is very alike reserved memory, reserved during
> > system boot time, not dynamically allocated at runtime.
> 
> Thanks for the clarification. The documentation is meant to be for the users, so
> I would suggest to drop the "-- Static memory, as parse of RAM reserved"
> because it doesn't add any value to know we treat the static memory and
> reserved memory the same way.
> 

Got it. Thx

> >>> +
> >>> +The dtb property should look like as follows:
> >>
> >> Do you mean "node" rather than "property"?
> >>
> >
> > Oh, sure. Maybe "as an example" shall be more clarified.
> 
> I would write "Below an example on how to specific the static memory region
> in the device-tree".
> 

Thanks for the example. Will do 

> >
> >>> +                compatible = "xen,domain";
> >>> +                #address-cells = <0x2>;
> >>> +                #size-cells = <0x2>;
> >>> +                cpus = <2>;
> >>> +                #xen,static-mem-address-cells = <0x1>;
> >>> +                #xen,static-mem-size-cells = <0x1>;
> >>> +                xen,static-mem = <0x30000000 0x20000000>;
> >>> +                ...
> >>> +            };
> >>> +        };
> >>> +    };
> >>> +
> >>> +DomU1 will have a static memory of 512MB reserved from the physical
> >>> +address
> >>> +0x30000000 to 0x50000000.
> >>
> >> I would write "This will reserve a 512MB region starting at the host
> >> physical address 0x30000000 to be exclusively used by DomU1".
> >>
> >
> > Sure, thx.
> >
> >>> diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c index
> >>> 476e32e0f5..d2714446e1 100644
> >>> --- a/xen/arch/arm/bootfdt.c
> >>> +++ b/xen/arch/arm/bootfdt.c
> >>> @@ -193,6 +193,55 @@ static int __init
> >> process_reserved_memory_node(const void *fdt, int node,
> >>>        return 0;
> >>>    }
> >>>
> >>> +static int __init process_static_memory(const void *fdt, int node,
> >>> +void *data) {
> >>
> >> This is pretty much a copy of process_memory_node(). So can we avoid
> >> the duplication?
> >>
> >> I think I mentionned it in the past but I can't find the outcome.
> >>
> >>> +    int i = 0, banks;
> >>> +    const __be32 *cell;
> >>> +    paddr_t start, size;
> >>> +    u32 address_cells, size_cells, reg_cells;
> >>> +    struct meminfo *mem = data;
> >>> +    const struct fdt_property *prop;
> >>> +
> >>> +
> >>> +    address_cells = device_tree_get_u32(fdt, node,
> >>> +                                        "#xen,static-mem-address-cells", 0);
> >>> +    size_cells = device_tree_get_u32(fdt, node,
> >>> +                                     "#xen,static-mem-size-cells", 0);
> >>> +    if ( (address_cells == 0) || (size_cells == 0) )
> >>> +    {
> >>> +         printk("Missing \"#xen,static-mem-address-cell\" or "
> >>> +                 "\"#xen,static-mem-address-cell\".\n");
> >>> +         return -EINVAL;
> >>> +    }
> >>> +    reg_cells = address_cells + size_cells;
> >>> +
> >>> +    prop = fdt_get_property(fdt, node, "xen,static-mem", NULL);
> >>> +    /*
> >>> +     * Static memory shall belong to a specific domain, that is,
> >>> +     * its node `domUx` has compatible string "xen,domain".
> >>> +     */
> >>
> >> This code is just checking the node compatible is "xen,domain". So I
> >> would drop the "domUx". This is also...
> >>
> >>> +    if ( fdt_node_check_compatible(fdt, node, "xen,domain") != 0 )
> >>> +    {
> >>> +        printk("xen,static-mem property can only be located under
> >>> + /domUx node.\n");
> >>
> >> ... not correct.
> >>
> >
> > I checked it here, to make sure the "xen,static-mem" property must be
> > used in a domain node, since for now, static memory could be only
> configured as guest RAM.
> >
> > Which part do you think it is not appropriate here?
> 
> You wrote "... can only be located under /domUx". That's not correct because
> we don't force (or even mention to) the user to name the node that way.
> 
> 
> >
> >>> +        return -EINVAL;
> >>> +    }
> >>> +
> >>> +    cell = (const __be32 *)prop->data;
> >>> +    banks = fdt32_to_cpu(prop->len) / (reg_cells * sizeof (u32));
> >>> +
> >>> +    for ( ; i < banks && mem->nr_banks < NR_MEM_BANKS; i++ )
> >>> +    {
> >>> +        device_tree_get_reg(&cell, address_cells, size_cells, &start, &size);
> >>> +        mem->bank[mem->nr_banks].start = start;
> >>> +        mem->bank[mem->nr_banks].size = size;
> >>> +        mem->nr_banks++;
> >>> +    }
> >>> +
> >>> +    if ( i < banks )
> >>> +        return -ENOSPC;
> >>> +    return 0;
> >>> +}
> >>> +
> >>>    static int __init process_reserved_memory(const void *fdt, int node,
> >>>                                              const char *name, int depth,
> >>>                                              u32 address_cells, u32
> >>> size_cells) @@ -346,6 +395,8 @@ static int __init
> >>> early_scan_node(const
> >> void *fdt,
> >>>            process_multiboot_node(fdt, node, name, address_cells, size_cells);
> >>>        else if ( depth == 1 && device_tree_node_matches(fdt, node,
> "chosen") )
> >>>            process_chosen_node(fdt, node, name, address_cells,
> >>> size_cells);
> >>> +    else if ( depth == 2 && fdt_get_property(fdt, node,
> >>> + "xen,static-mem", NULL) )
> >>
> >> How about checking the compatible instead?
> >>
> >
> > hmm, since it is a property, not a node. so...
> Right, but you could write:
> 
> device_tree_node_compatible(fdt, node, "xen,domain")
> 
> This would be more correct because we are interested in node using the Xen
> domain binding that contains the property "xen,static-mem".
> 
> All the other nodes with the property "xen,static-mem" should be left alone
> because it may have a different meaning.
> 

True, true. Will do

> Cheers,
> 
> --
> Julien Grall