On Thu, 17 Dec 2025, Oleksandr Tyshchenko wrote: > On 18.12.25 02:05, Stefano Stabellini wrote: > Hello Stefano > > > On Wed, 17 Dec 2025, Oleksandr Tyshchenko wrote: > >> Creating a dom0less guest with a high vCPU count (e.g., >32) fails > >> because the fixed 4KiB device tree buffer (DOMU_DTB_SIZE) overflows > >> during creation. > >> > >> The FDT nodes for each vCPU are the primary consumer of space, > >> and the previous fixed-size buffer was insufficient. > >> > >> This patch replaces the fixed size with a formula that calculates > >> the required buffer size based on a fixed baseline plus a scalable > >> portion for each potential vCPU up to the MAX_VIRT_CPUS limit. > >> > >> Please note, the change to DOMU_DTB_SIZE formula would result in > >> a smaller buffer size of 3072 bytes compared to the original 4096 bytes > >> on Arm32 platforms where MAX_VIRT_CPUS is 8. > > > > I am OK with this patch I would only ask to retain the minimum size of > > 4KB due to the possible presence of passthrough device nodes. > > I think there might be cases when even 4KB would not be enough to cover > the whole dtb with passthrough device nodes. But the existing code > should already handle that, so if a partial device tree is provided, > then it will be accounted separately: > > /* Account for domU passthrough DT size */ > if ( kinfo->dtb ) > fdt_size += kinfo->dtb->size;
I forgot about this. In that case: Acked-by: Stefano Stabellini <[email protected]>
