Re: [PATCH] x86/pvh: pass module command line to dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.01.2021 10:05, Roger Pau Monne wrote:
> Both the multiboot and the HVM start info structures allow passing a
> string together with a module. Implement the missing support in
> pvh_load_kernel so that module strings found in the multiboot
> structure are forwarded to dom0.
> 
> Fixes: 62ba982424 ('x86: parse Dom0 kernel for PVHv2')

This really is relevant only when it's not an initrd which gets
passed as module, I suppose? I'm not fully convinced I'd call
this a bug then, but perhaps more a missing feature. Which in
turn means I'm not sure about the change's disposition wrt 4.15.
Cc-ing Ian.

> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Albeit ...

> --- a/xen/arch/x86/hvm/dom0_build.c
> +++ b/xen/arch/x86/hvm/dom0_build.c
> @@ -617,7 +617,21 @@ static int __init pvh_load_kernel(struct domain *d, 
> const module_t *image,
>  
>          mod.paddr = last_addr;
>          mod.size = initrd->mod_end;
> -        last_addr += ROUNDUP(initrd->mod_end, PAGE_SIZE);
> +        last_addr += ROUNDUP(initrd->mod_end, elf_64bit(&elf) ? 8 : 4);
> +        if ( initrd->string )
> +        {
> +            char *str = __va(initrd->string);
> +
> +            rc = hvm_copy_to_guest_phys(last_addr, str, strlen(str) + 1, v);
> +            if ( rc )
> +            {
> +                printk("Unable to copy module command line\n");
> +                return rc;
> +            }
> +            mod.cmdline_paddr = last_addr;
> +            last_addr += strlen(str) + 1;

... it would have been nice if this length was calculated just
once, into a local variable. I'd be fine making the adjustment
while committing, so long as you agree.

Jan