Paul Mackerras <pau...@ozlabs.org> writes:
> Currently, if the kernel is running on a POWER9 processor under a
> hypervisor, it will try to use the radix MMU even though it doesn't
> have the necessary code to use radix under a hypervisor (it doesn't
> negotiate use of radix, and it doesn't do the H_REGISTER_PROC_TBL
> hcall). The result is that the guest kernel will crash when it tries
> to turn on the MMU, because it will still actually be using the HPT
> MMU, but it won't have set up any SLB or HPT entries. It does this
> because the only thing that the kernel looks at in deciding to use
> radix, on any platform, is the ibm,pa-features property on the cpu
> device nodes.
>
> This fixes it by looking for the /chosen/ibm,architecture-vec-5
> property, and if it exists, clearing the radix MMU feature bit.
> We do this before we decide whether to initialize for radix or HPT.
> This property is created by the hypervisor as a result of the guest
> calling the ibm,client-architecture-support method to indicate
> its capabilities, so it only exists on systems with a hypervisor.
> The reason for using this property is that in future, when we
> have support for using radix under a hypervisor, we will need
> to check this property to see whether the hypervisor agreed to
> us using radix.
Hypervisor that doesn't support radix should clear the ibm,pa-features
radix feature bit right ? We look at that before setting
MMU_FTR_TYPE_RADIX. So how did we end up enabling radix in the above
case ?
>
> Fixes: 17a3dd2f5fc7 ("powerpc/mm/radix: Use firmware feature to enable Radix
> MMU")
> Cc: sta...@vger.kernel.org # v4.7+
> Signed-off-by: Paul Mackerras <pau...@ozlabs.org>
> ---
> arch/powerpc/mm/init_64.c | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> index a000c35..098531d 100644
> --- a/arch/powerpc/mm/init_64.c
> +++ b/arch/powerpc/mm/init_64.c
> @@ -42,6 +42,8 @@
> #include <linux/memblock.h>
> #include <linux/hugetlb.h>
> #include <linux/slab.h>
> +#include <linux/of_fdt.h>
> +#include <linux/libfdt.h>
>
> #include <asm/pgalloc.h>
> #include <asm/page.h>
> @@ -344,6 +346,28 @@ static int __init parse_disable_radix(char *p)
> }
> early_param("disable_radix", parse_disable_radix);
>
> +/*
> + * If we're running under a hypervisor, we currently can't do radix
> + * since we don't have the code to do the H_REGISTER_PROC_TBL hcall.
> + * We tell that we're running under a hypervisor by looking for the
> + * /chosen/ibm,architecture-vec-5 property.
> + */
> +static void early_check_vec5(void)
> +{
> + unsigned long root, chosen;
> + int size;
> + const u8 *vec5;
> +
> + root = of_get_flat_dt_root();
> + chosen = of_get_flat_dt_subnode_by_name(root, "chosen");
> + if (chosen == -FDT_ERR_NOTFOUND)
> + return;
> + vec5 = of_get_flat_dt_prop(chosen, "ibm,architecture-vec-5", &size);
> + if (!vec5)
> + return;
> + cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
> +}
> +
> void __init mmu_early_init_devtree(void)
> {
> /* Disable radix mode based on kernel command line. */
> @@ -351,6 +375,9 @@ void __init mmu_early_init_devtree(void)
> cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
>
> if (early_radix_enabled())
> + early_check_vec5();
> +
> + if (early_radix_enabled())
> radix__early_init_devtree();
> else
> hash__early_init_devtree();
> --
> 2.7.4
