This is a note to let you know that I've just added the patch titled arm64: mm: use a 48-bit ID map when possible on 52-bit VA builds to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: arm64-mm-use-a-48-bit-id-map-when-possible-on-52-bit.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 65fe43f84bceaf6e1d3b796231f81d2470a9e9e1 Author: Ard Biesheuvel <ardb@xxxxxxxxxx> Date: Wed Mar 10 18:15:11 2021 +0100 arm64: mm: use a 48-bit ID map when possible on 52-bit VA builds [ Upstream commit 7ba8f2b2d652cd8d8a2ab61f4be66973e70f9f88 ] 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@xxxxxxxxxx> Link: http://lore.kernel.org/r/20210310003216.410037-1-msalter@xxxxxxxxxx Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> Link: https://lore.kernel.org/r/20210310171515.416643-2-ardb@xxxxxxxxxx Signed-off-by: Will Deacon <will@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h index 3827ff4040a3..3a5d9f1c91b6 100644 --- a/arch/arm64/include/asm/mmu_context.h +++ b/arch/arm64/include/asm/mmu_context.h @@ -63,10 +63,7 @@ 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)); } /* diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 438de2301cfe..a2e0b3754943 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -337,7 +337,7 @@ __create_page_tables: */ adrp x5, __idmap_text_end clz x5, x5 - cmp x5, TCR_T0SZ(VA_BITS) // default T0SZ small enough? + cmp x5, TCR_T0SZ(VA_BITS_MIN) // default T0SZ small enough? b.ge 1f // .. then skip VA range extension adr_l x6, idmap_t0sz diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index d10247fab0fd..99bc0289ab2b 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -38,7 +38,7 @@ #define NO_BLOCK_MAPPINGS BIT(0) #define NO_CONT_MAPPINGS BIT(1) -u64 idmap_t0sz = TCR_T0SZ(VA_BITS); +u64 idmap_t0sz = TCR_T0SZ(VA_BITS_MIN); u64 idmap_ptrs_per_pgd = PTRS_PER_PGD; u64 __section(".mmuoff.data.write") vabits_actual;