[edk2-devel] [PATCH] ArmVirtPkg/ArmVirtQemu: Avoid early ID map on ThunderX
Ard Biesheuvel
ardb at kernel.org
Thu Jan 5 11:46:19 UTC 2023
On Wed, 4 Jan 2023 at 18:23, Ard Biesheuvel <ardb at kernel.org> wrote:
>
> The early ID map used by ArmVirtQemu uses ASID scoped non-global
> mappings, as this allows us to switch to the permanent ID map seamlessly
> without the need for explicit TLB maintenance.
>
> However, this triggers a known erratum on ThunderX, which does not
> tolerate non-global mappings that are executable at EL1, as this appears
> to result in I-cache corruption. (Linux disables the KPTI based Meltdown
> mitigation on ThunderX for the same reason)
>
> So work around this, by detecting the CPU implementor and part number,
> and proceeding without the early ID map if a ThunderX CPU is detected.
>
> Note that this requires the C code to be built with strict alignment
> again, as we may end up executing it with the MMU and caches off.
>
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
> ArmVirtPkg/ArmVirtQemu.dsc | 6 ++++++
> ArmVirtPkg/Library/ArmPlatformLibQemu/AArch64/ArmPlatformHelper.S | 18 ++++++++++++++++++
> 2 files changed, 24 insertions(+)
>
> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
> index f77443229e8e..340b36f69c2c 100644
> --- a/ArmVirtPkg/ArmVirtQemu.dsc
> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
> @@ -31,6 +31,7 @@ [Defines]
> DEFINE SECURE_BOOT_ENABLE = FALSE
> DEFINE TPM2_ENABLE = FALSE
> DEFINE TPM2_CONFIG_ENABLE = FALSE
> + DEFINE CAVIUM_ERRATUM_27456 = FALSE
>
> #
> # Network definition
> @@ -117,7 +118,12 @@ [LibraryClasses.common.UEFI_DRIVER]
> UefiScsiLib|MdePkg/Library/UefiScsiLib/UefiScsiLib.inf
>
> [BuildOptions]
> +!if $(CAVIUM_ERRATUM_27456) == TRUE
> + GCC:*_*_AARCH64_CC_XIPFLAGS = -mno-strict-align
This is wrong - this should be '-mstrict-align'
> + GCC:*_*_AARCH64_PP_FLAGS = -DCAVIUM_ERRATUM_27456
> +!else
> GCC:*_*_AARCH64_CC_XIPFLAGS ==
> +!endif
>
> !include NetworkPkg/NetworkBuildOptions.dsc.inc
>
> diff --git a/ArmVirtPkg/Library/ArmPlatformLibQemu/AArch64/ArmPlatformHelper.S b/ArmVirtPkg/Library/ArmPlatformLibQemu/AArch64/ArmPlatformHelper.S
> index 05ccc7f9f043..962f1ba3a4d7 100644
> --- a/ArmVirtPkg/Library/ArmPlatformLibQemu/AArch64/ArmPlatformHelper.S
> +++ b/ArmVirtPkg/Library/ArmPlatformLibQemu/AArch64/ArmPlatformHelper.S
> @@ -44,8 +44,26 @@
>
>
> ASM_FUNC(ArmPlatformPeiBootAction)
> +#ifdef CAVIUM_ERRATUM_27456
> + /*
> + * On Cavium ThunderX, using non-global mappings that are executable at EL1
> + * results in I-cache corruption. So just avoid the early ID mapping there.
> + *
> + * MIDR implementor 0x43
> + * MIDR part numbers 0xA1 0xA2
> + */
> + mrs x0, midr_el1 // read the MIDR into X0
> + ubfx x1, x0, #6, #10 // grab part number bits [11:2]
> + ubfx x0, x0, #24, #8 // grab implementor id
> + mov x2, #0xA0 >> 2
> + cmp x0, #0x43 // compare implementor id
> + ccmp x1, x2, #0, eq // compare part# bits [11:2]
> + b.eq .Lreturn
> +#endif
> +
> mrs x0, CurrentEL // check current exception level
> tbz x0, #3, 0f // bail if above EL1
> +.Lreturn:
> ret
>
> 0:mov_i x0, mairval
> --
> 2.39.0
>
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