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authorArd Biesheuvel <ardb@kernel.org>2021-03-10 18:15:11 +0100
committerWill Deacon <will@kernel.org>2021-03-11 13:04:28 +0000
commit7ba8f2b2d652cd8d8a2ab61f4be66973e70f9f88 (patch)
tree85b24dcd8d1f5b89def949ad4306bc54b9d46182 /arch/arm64/include
parent7bb8bc6eb550116c504fb25af8678b9d7ca2abc5 (diff)
arm64: mm: use a 48-bit ID map when possible on 52-bit VA builds
52-bit VA kernels can run on hardware that is only 48-bit capable, but configure the ID map as 52-bit by default. This was not a problem until recently, because the special T0SZ value for a 52-bit VA space was never programmed into the TCR register anwyay, and because a 52-bit ID map happens to use the same number of translation levels as a 48-bit one. This behavior was changed by commit 1401bef703a4 ("arm64: mm: Always update TCR_EL1 from __cpu_set_tcr_t0sz()"), which causes the unsupported T0SZ value for a 52-bit VA to be programmed into TCR_EL1. While some hardware simply ignores this, Mark reports that Amberwing systems choke on this, resulting in a broken boot. But even before that commit, the unsupported idmap_t0sz value was exposed to KVM and used to program TCR_EL2 incorrectly as well. Given that we already have to deal with address spaces being either 48-bit or 52-bit in size, the cleanest approach seems to be to simply default to a 48-bit VA ID map, and only switch to a 52-bit one if the placement of the kernel in DRAM requires it. This is guaranteed not to happen unless the system is actually 52-bit VA capable. Fixes: 90ec95cda91a ("arm64: mm: Introduce VA_BITS_MIN") Reported-by: Mark Salter <msalter@redhat.com> Link: http://lore.kernel.org/r/20210310003216.410037-1-msalter@redhat.com Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20210310171515.416643-2-ardb@kernel.org Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/include')
-rw-r--r--arch/arm64/include/asm/mmu_context.h5
1 files changed, 1 insertions, 4 deletions
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index 70ce8c1d2b07..0f467d550f27 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -65,10 +65,7 @@ extern u64 idmap_ptrs_per_pgd;
static inline bool __cpu_uses_extended_idmap(void)
{
- if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52))
- return false;
-
- return unlikely(idmap_t0sz != TCR_T0SZ(VA_BITS));
+ return unlikely(idmap_t0sz != TCR_T0SZ(vabits_actual));
}
/*