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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200329141258.31172-1-ardb@kernel.org> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200330_065806_913323_ED8A34D9 X-CRM114-Status: GOOD ( 26.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, catalin.marinas@arm.com, will@kernel.org, kernel-hardening@lists.openwall.com Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 3/29/20 10:12 AM, Ard Biesheuvel wrote: > When CONFIG_DEBUG_ALIGN_RODATA is enabled, kernel segments mapped with > different permissions (r-x for .text, r-- for .rodata, rw- for .data, > etc) are rounded up to 2 MiB so they can be mapped more efficiently. > In particular, it permits the segments to be mapped using level 2 > block entries when using 4k pages, which is expected to result in less > TLB pressure. > > However, the mappings for the bulk of the kernel will use level 2 > entries anyway, and the misaligned fringes are organized such that they > can take advantage of the contiguous bit, and use far fewer level 3 > entries than would be needed otherwise. > > This makes the value of this feature dubious at best, and since it is not > enabled in defconfig or in the distro configs, it does not appear to be > in wide use either. So let's just remove it. > This was supposed to avoid potential performance inconsistencies with some memory being in pages vs other in block. It was always a minor concern so if it's preventing other work: Acked-by: Laura Abbott > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/Kconfig.debug | 13 ------------- > arch/arm64/include/asm/memory.h | 12 +----------- > drivers/firmware/efi/libstub/arm64-stub.c | 8 +++----- > 3 files changed, 4 insertions(+), 29 deletions(-) > > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug > index 1c906d932d6b..a1efa246c9ed 100644 > --- a/arch/arm64/Kconfig.debug > +++ b/arch/arm64/Kconfig.debug > @@ -52,19 +52,6 @@ config DEBUG_WX > > If in doubt, say "Y". > > -config DEBUG_ALIGN_RODATA > - depends on STRICT_KERNEL_RWX > - bool "Align linker sections up to SECTION_SIZE" > - help > - If this option is enabled, sections that may potentially be marked as > - read only or non-executable will be aligned up to the section size of > - the kernel. This prevents sections from being split into pages and > - avoids a potential TLB penalty. The downside is an increase in > - alignment and potentially wasted space. Turn on this option if > - performance is more important than memory pressure. > - > - If in doubt, say N. > - > config DEBUG_EFI > depends on EFI && DEBUG_INFO > bool "UEFI debugging" > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index 4d94676e5a8b..3b34f7bde2f2 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -119,22 +119,12 @@ > > /* > * Alignment of kernel segments (e.g. .text, .data). > - */ > -#if defined(CONFIG_DEBUG_ALIGN_RODATA) > -/* > - * 4 KB granule: 1 level 2 entry > - * 16 KB granule: 128 level 3 entries, with contiguous bit > - * 64 KB granule: 32 level 3 entries, with contiguous bit > - */ > -#define SEGMENT_ALIGN SZ_2M > -#else > -/* > + * > * 4 KB granule: 16 level 3 entries, with contiguous bit > * 16 KB granule: 4 level 3 entries, without contiguous bit > * 64 KB granule: 1 level 3 entry > */ > #define SEGMENT_ALIGN SZ_64K > -#endif > > /* > * Memory types available. > diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c > index db0c1a9c1699..fc9f8ab533a7 100644 > --- a/drivers/firmware/efi/libstub/arm64-stub.c > +++ b/drivers/firmware/efi/libstub/arm64-stub.c > @@ -75,14 +75,12 @@ efi_status_t handle_kernel_image(unsigned long *image_addr, > > if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) { > /* > - * If CONFIG_DEBUG_ALIGN_RODATA is not set, produce a > - * displacement in the interval [0, MIN_KIMG_ALIGN) that > - * doesn't violate this kernel's de-facto alignment > + * Produce a displacement in the interval [0, MIN_KIMG_ALIGN) > + * that doesn't violate this kernel's de-facto alignment > * constraints. > */ > u32 mask = (MIN_KIMG_ALIGN - 1) & ~(EFI_KIMG_ALIGN - 1); > - u32 offset = !IS_ENABLED(CONFIG_DEBUG_ALIGN_RODATA) ? > - (phys_seed >> 32) & mask : TEXT_OFFSET; > + u32 offset = (phys_seed >> 32) & mask; > > /* > * With CONFIG_RANDOMIZE_TEXT_OFFSET=y, TEXT_OFFSET may not > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel