Re: [Query] Unable to probe reserved-memory carveouts in DomU with Xen

["Orzel, Michal" <michal.orzel@xxxxxxx>]

Hi,

I'm afraid this will not work. The reason is that Xen only copies nodes from the
passthrough DTB to final DTB that are placed under `/passthrough` node and
`/aliases`. /reserved-memory needs to be under root node `/`, therefore it will
not be copied. However, it seems like you are not using CMA node specifying a
fixed memory region (using `reg`) but size. In that case you should be able to
achieve the same using `cma=128M` kernel cmdline parameter.

~Michal

On 24-Jul-26 08:55, Beleswar Prasad Padhi wrote:
> Hi all,
> 
> I have been trying to use reserved-memory carveouts in DomU, but failing 
> constantly.
> 
> This is the log from Dom1 boot:
> 
> [    0.000000] earlycon: uart8250 at MMIO32 0x0000000053914000 (options 
> '115200n
> 8')
> [    0.000000] printk: legacy bootconsole [uart8250] enabled
> [    0.000000] Xen 4.21 support found
> [    0.000000] efi: UEFI not found.
> *[    0.000000] OF: reserved mem: Reserved memory: No reserved-memory node in 
> the DT*
> [    0.000000] Zone ranges:
> [    0.000000]   DMA      [mem 0x0000000040000000-0x0000000051ffffff]
> [    0.000000]   DMA32    empty
> [    0.000000]   Normal   empty
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000040000000-0x0000000051ffffff]
> [    0.000000] Initmem setup node 0 [mem 
> 0x0000000040000000-0x0000000051ffffff]
> [    0.000000] On node 0, zone DMA: 24576 pages in unavailable ranges
> [    0.000000] cma: Reserved 32 MiB at 0x000000004f800000
> 
> This is my passthrough.dts:
> 
>     1 /*
>     2 * This is a partial DT for passthrough node to DomU.
>     3 */
>     4 #include <dt-bindings/interrupt-controller/irq.h>
>     5 #include <dt-bindings/interrupt-controller/arm-gic.h>
>     6 
>     7 /dts-v1/;
>     8 
>     9 / {
>    10         #address-cells = <2>;
>    11         #size-cells = <1>;
>    12 
> ~  13         reserved-memory {
> ~  14                 #address-cells = <2>;
> ~  15                 #size-cells = <2>;
> +  16                 ranges;
> +  17 
> +  18                 /* CMA region for framebuffer allocation */
> +  19                 linux,cma {
> +  20                         compatible = "shared-dma-pool";
> +  21                         reusable;
> +  22                         size = <0x00 0x08000000>; /* 128MB CMA pool */
> +  23                         linux,cma-default;
> +  24                 };
>    25         };
>    26 
>    27         passthrough {
>    28                 compatible = "simple-bus";
>    29                 ranges;
>    30                 #address-cells = <2>;
>    31                 #size-cells = <1>;
>    32 
>    33                 misc_clk: misc_clk {
>    34                         #clock-cells = <0>;
>    35                         clock-frequency = <100000000>;
>    36                         compatible = "fixed-clock";
>    37                 };
> 
>    73                 uart@53914000 {
>    74                         compatible = "ns16550a";
>    75                         reg = <0x00 0x53914000 0x1000>;
> ~_ 76                         interrupts = <0 302 4>;
>    77                         reg-shift = <2>;
>    78                         reg-io-width = <4>;
>    79                         clocks = <&misc_clk>;
>    80                         oversampling-rate = <16>;
>    81                         programmable-char-timeout = <4>;
>    82                         status = "okay";
>    83                         xen,path = 
> "/bus@100000/bus@22000000/uart@53914000";
>    84                         xen,reg = <0x0 0x53914000 0x1000 0x0 
> 0x53914000>;
>    85                         xen,force-assign-without-iommu;
>    86                 };
>    87          };
> 
>    88    };
> 
> 
> And this is my dom1.cfg file:
> 
>  1 name = "dom1"
>  2 memory = 256
>  3 vcpus = 4
>  4 
>  5 kernel = "/boot/xen-dom1/Image"
>  6 extra = "console=ttyS0,115200n8 
> earlycon=uart8250,mmio32,0x53914000,115200n8 loglevel=8 root=/dev/xvda rw"
>  7 
>  8 # UART1 (0x53914000) passthrough to Dom1 console
>  9 iomem = ["0x53914,1"]
> 11 irqs = [ 334 ]
> 12 dtdev = [ "/bus@100000/bus@22000000/uart@53914000"]
> 13 vif = ["script=vif-route"]
> 14 device_tree = "/boot/xen-dom1/passthrough.dtb"
> 15 #  
> 17 disk = ["phy:/dev/vda2,xvda,rw"]
> 
> 
> Am I doing something wrong? Any help or debugging leads would be really 
> appreciated...
> 
> Thank you,
> Beleswar
> 
>