Re: [PATCH] xen/arm: Add workaround for Cortex-A53 erratum #843419

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Luca,

> On 10 Dec 2020, at 10:42, Luca Fancellu <Luca.Fancellu@xxxxxxx> wrote:
> 
> On the Cortex A53, when executing in AArch64 state, a load or store 
> instruction
> which uses the result of an ADRP instruction as a base register, or which uses
> a base register written by an instruction immediately after an ADRP to the
> same register, might access an incorrect address.
> 
> The workaround is to enable the linker flag --fix-cortex-a53-843419
> if present, to check and fix the affected sequence. Otherwise print a warning
> that Xen may be susceptible to this errata
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Thanks
Cheers
Bertrand

> ---
> docs/misc/arm/silicon-errata.txt |  1 +
> xen/arch/arm/Kconfig             | 19 +++++++++++++++++++
> xen/arch/arm/Makefile            |  8 ++++++++
> xen/scripts/Kbuild.include       | 12 ++++++++++++
> 4 files changed, 40 insertions(+)
> 
> diff --git a/docs/misc/arm/silicon-errata.txt 
> b/docs/misc/arm/silicon-errata.txt
> index 27bf957ebf..1925d8fd4e 100644
> --- a/docs/misc/arm/silicon-errata.txt
> +++ b/docs/misc/arm/silicon-errata.txt
> @@ -45,6 +45,7 @@ stable hypervisors.
> | ARM            | Cortex-A53      | #827319         | ARM64_ERRATUM_827319   
>  |
> | ARM            | Cortex-A53      | #824069         | ARM64_ERRATUM_824069   
>  |
> | ARM            | Cortex-A53      | #819472         | ARM64_ERRATUM_819472   
>  |
> +| ARM            | Cortex-A53      | #843419         | ARM64_ERRATUM_843419  
>   |
> | ARM            | Cortex-A55      | #1530923        | N/A                    
>  |
> | ARM            | Cortex-A57      | #852523         | N/A                    
>  |
> | ARM            | Cortex-A57      | #832075         | ARM64_ERRATUM_832075   
>  |
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index f5b1bcda03..41bde2f401 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -186,6 +186,25 @@ config ARM64_ERRATUM_819472
> 
>         If unsure, say Y.
> 
> +config ARM64_ERRATUM_843419
> +     bool "Cortex-A53: 843419: A load or store might access an incorrect 
> address"
> +     default y
> +     depends on ARM_64
> +     help
> +       This option adds an alternative code sequence to work around ARM
> +       erratum 843419 on Cortex-A53 parts up to r0p4.
> +
> +       When executing in AArch64 state, a load or store instruction which 
> uses
> +       the result of an ADRP instruction as a base register, or which uses a
> +       base register written by an instruction immediately after an ADRP to 
> the
> +       same register, might access an incorrect address.
> +
> +       The workaround enables the linker to check if the affected sequence is
> +       produced and it will fix it with an alternative not affected sequence
> +       that produce the same behavior.
> +
> +       If unsure, say Y.
> +
> config ARM64_ERRATUM_832075
>       bool "Cortex-A57: 832075: possible deadlock on mixing exclusive memory 
> accesses with device loads"
>       default y
> diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
> index 296c5e68bb..ad2d497c45 100644
> --- a/xen/arch/arm/Makefile
> +++ b/xen/arch/arm/Makefile
> @@ -101,6 +101,14 @@ prelink.o: $(ALL_OBJS) FORCE
>       $(call if_changed,ld)
> endif
> 
> +ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
> +    ifeq ($(call ld-option, --fix-cortex-a53-843419),n)
> +        $(warning ld does not support --fix-cortex-a53-843419; xen may be 
> susceptible to erratum)
> +    else
> +        XEN_LDFLAGS += --fix-cortex-a53-843419
> +    endif
> +endif
> +
> targets += prelink.o
> 
> $(TARGET)-syms: prelink.o xen.lds
> diff --git a/xen/scripts/Kbuild.include b/xen/scripts/Kbuild.include
> index e62eddc365..83c7e1457b 100644
> --- a/xen/scripts/Kbuild.include
> +++ b/xen/scripts/Kbuild.include
> @@ -43,6 +43,18 @@ define as-option-add-closure
>     endif
> endef
> 
> +# $(if-success,<command>,<then>,<else>)
> +# Return <then> if <command> exits with 0, <else> otherwise.
> +if-success = $(shell { $(1); } >/dev/null 2>&1 && echo "$(2)" || echo "$(3)")
> +
> +# $(success,<command>)
> +# Return y if <command> exits with 0, n otherwise
> +success = $(call if-success,$(1),y,n)
> +
> +# $(ld-option,<flag>)
> +# Return y if the linker supports <flag>, n otherwise
> +ld-option = $(call success,$(LD) -v $(1))
> +
> # cc-ifversion
> # Usage:  EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
> cc-ifversion = $(shell [ $(CONFIG_GCC_VERSION)0 $(1) $(2)000 ] && echo $(3) 
> || echo $(4))
> -- 
> 2.17.1
>