Re: [PATCH 12/15] x86/PVH: heed the kernel in pvh_steal_ram()

[Roger Pau Monné <roger@xxxxxxxxxxxxxx>]

On Mon, Oct 12, 2026 at 10:25:40AM +0200, Jan Beulich wrote:
> While the function working downwards will typically result in no conflict
> with the kernel range, there's no guarantee of that.
> 
> Fixes: 1d74282c455f ("x86: setup PVHv2 Dom0 ACPI tables")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/arch/x86/hvm/dom0_build.c
> +++ b/xen/arch/x86/hvm/dom0_build.c
> @@ -186,8 +186,12 @@ static int __init pvh_populate_memory_ra
>  /* Steal RAM from the end of a memory region. */
>  static int __init pvh_steal_ram(struct domain *d, unsigned long size,
>                                  unsigned long align, paddr_t limit,
> +                                const struct elf_binary *elf,
>                                  paddr_t *addr)
>  {
> +    paddr_t kernel_start = (paddr_t)elf->dest_base & PAGE_MASK;
> +    paddr_t kernel_end = ROUNDUP((paddr_t)elf->dest_base + elf->dest_size,
> +                                 PAGE_SIZE);
>      unsigned int i = d->arch.nr_e820;
>  
>      /*
> @@ -203,6 +207,11 @@ static int __init pvh_steal_ram(struct d
>              continue;
>  
>          *addr = (entry->addr + entry->size - size) & ~(align - 1);
> +
> +        /* Avoid kernel range, if this is the region it lives in. */
> +        if ( *addr < kernel_end && *addr + size > kernel_start )
> +            *addr = (kernel_start - size) & ~(align - 1);
> +
>          if ( *addr < entry->addr ||
>               /* Don't steal from the low 1MB due to the copying done there. 
> */
>               *addr < MB(1) )

If you clip addr to remove the kernel range for allocation purposes
you need to restore it before the `entry->size = *addr - entry->addr`
adjustment.

Overall I continue to think this will be much simpler if we passed
around a rangeset.  This series is adding a fair amount of extra code
to deal with overlaps between kernel/initrd allocations vs everything
else, which could be solved more easily by using a rangeset.

Thanks, Roger.