On 16 Jun 2022, at 8:00, Michael Ellerman wrote:
> After commit 11ac3e87ce09 ("mm: cma: use pageblock_order as the single
> alignment") there is an error at boot about the KVM CMA reservation
> failing, eg:
>
> kvm_cma_reserve: reserving 6553 MiB for global area
> cma: Failed to reserve 6553 MiB
>
> That makes it impossible to start KVM guests using the hash MMU with
> more than 2G of memory, because the VM is unable to allocate a large
> enough region for the hash page table, eg:
>
> $ qemu-system-ppc64 -enable-kvm -M pseries -m 4G ...
> qemu-system-ppc64: Failed to allocate KVM HPT of order 25: Cannot allocate memory
>
> Aneesh pointed out that this happens because when kvm_cma_reserve() is
> called, pageblock_order has not been initialised yet, and is still zero,
> causing the checks in cma_init_reserved_mem() against
> CMA_MIN_ALIGNMENT_PAGES to fail.
>
> Fix it by moving the call to kvm_cma_reserve() after initmem_init(). The
> pageblock_order is initialised in sparse_init() which is called from
> initmem_init().
>
> Also move the hugetlb CMA reservation.
>
> Fixes: 11ac3e87ce09 ("mm: cma: use pageblock_order as the single alignment")
> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> ---
> arch/powerpc/kernel/setup-common.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index eb0077b302e2..1a02629ec70b 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -935,12 +935,6 @@ void __init setup_arch(char **cmdline_p)
> /* Print various info about the machine that has been gathered so far. */
> print_system_info();
>
> - /* Reserve large chunks of memory for use by CMA for KVM. */
> - kvm_cma_reserve();
> -
> - /* Reserve large chunks of memory for us by CMA for hugetlb */
> - gigantic_hugetlb_cma_reserve();
> -
> klp_init_thread_info(&init_task);
>
> setup_initial_init_mm(_stext, _etext, _edata, _end);
> @@ -955,6 +949,13 @@ void __init setup_arch(char **cmdline_p)
>
> initmem_init();
>
> + /*
> + * Reserve large chunks of memory for use by CMA for KVM and hugetlb. These must
> + * be called after initmem_init(), so that pageblock_order is initialised.
> + */
> + kvm_cma_reserve();
> + gigantic_hugetlb_cma_reserve();
> +
> early_memtest(min_low_pfn << PAGE_SHIFT, max_low_pfn << PAGE_SHIFT);
>
> if (ppc_md.setup_arch)
> --
> 2.35.3
Thank you for the fix.
Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
--
Best Regards,
Yan, Zi
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