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SubjectRe: [PATCH v1 2/2] acpi, x86: Remove encryption mask from ACPI page protection type

* Tom Lendacky <thomas.lendacky@amd.com> wrote:

> The function arch_apei_get_mem_attributes() is used to set the page
> protection type for ACPI physical addresses. When SME is active, the
> associated protection type needs to not have the encryption mask set
> since the ACPI tables live in un-encrypted memory. Modify the
> arch_apei_get_mem_attributes() function to remove the encryption mask
> when SME is active by returning the PAGE_KERNEL_IO protection type.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> arch/x86/include/asm/acpi.h | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> index 562286f..89df39d 100644
> --- a/arch/x86/include/asm/acpi.h
> +++ b/arch/x86/include/asm/acpi.h
> @@ -34,6 +34,7 @@
>
> #ifdef CONFIG_ACPI_APEI
> # include <asm/pgtable_types.h>
> +# include <linux/mem_encrypt.h>
> #endif
>
> #ifdef CONFIG_ACPI
> @@ -164,8 +165,12 @@ static inline pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
> * anything other than PAGE_KERNEL (some arm64 platforms
> * require the equivalent of PAGE_KERNEL_NOCACHE), return that
> * until we know differently.
> + *
> + * When SME is active, the ACPI information will not reside in
> + * in memory in an encrypted state so return a protection attribute
> + * that does not have the encryption bit set.
> */
> - return PAGE_KERNEL;
> + return sme_active() ? PAGE_KERNEL_IO : PAGE_KERNEL;

'in in memory'?

Also, this seems a bit ad-hoc to me. What are the rules for what is encrypted and
what is not?

I presume the main rule is that everything that was written before the kernel
activates SME, and which the kernel will read later on, is unencrypted -
everything else is encrypted. Is that correct?

How about things like kexec creating a separate mptable for the kexec kernel -
would that code have to create unencrypted data? See
e820__memblock_alloc_reserved() and related code.

Thanks,

Ingo

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