On Thu, Jan 12, 2017 at 08:07:09PM +1100, Paul Mackerras wrote:
> 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
H_REGISTER_PROCESS_TABLE
for consistency
> hcall). The result is that the guest kernel will crash when it tries
> to turn on the MMU.
>
> This fixes it by looking for the /chosen/ibm,architecture-vec-5
> property, and if it exists, clears the radix MMU feature bit,
> 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 will indicate whether the hypervisor
> agreed to us using radix.
>
> Systems without a hypervisor may have this property also (for
> example, skiboot creates it), so we check the HV bit in the MSR
> to see whether we are running as a guest or not. If we are in
> hypervisor mode, then we can do whatever we like including
> using the radix MMU.
>
> 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.
>
> Cc: stable@xxxxxxxxxxxxxxx # v4.8+
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
> ---
> arch/powerpc/mm/init_64.c | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> index 93abf8a..4d9481e 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>
> @@ -344,12 +346,43 @@ 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.
_PROCESS_TABLE
> + * 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)
> +{
The function is called early_check, but it also disables MMU_FTR_TYPE_RADIX,
should the disabling be moved out to the caller, since the check has
nothing to do with disabling the feature?
> + 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. */
> if (disable_radix)
> cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
>
> + /*
> + * Check /chosen/ibm,architecture-vec-5 if running as a guest.
> + * When running bare-metal, we can use radix if we like
> + * even though the ibm,architecture-vec-5 property created by
> + * skiboot doesn't have the necessary bits set.
> + */
> + if (early_radix_enabled() && !(mfmsr() & MSR_HV))
> + early_check_vec5();
Balbir Singh.
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