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SubjectRe: [RFC PATCH v3 15/20] x86: Check for memory encryption on the APs
On Wed, Nov 09, 2016 at 06:37:40PM -0600, Tom Lendacky wrote:
> Add support to check if memory encryption is active in the kernel and that
> it has been enabled on the AP. If memory encryption is active in the kernel
> but has not been enabled on the AP then do not allow the AP to continue
> start up.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> arch/x86/include/asm/realmode.h | 12 ++++++++++++
> arch/x86/realmode/init.c | 4 ++++
> arch/x86/realmode/rm/trampoline_64.S | 19 +++++++++++++++++++
> 3 files changed, 35 insertions(+)
>
> diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
> index 230e190..850dbe0 100644
> --- a/arch/x86/include/asm/realmode.h
> +++ b/arch/x86/include/asm/realmode.h
> @@ -1,6 +1,15 @@
> #ifndef _ARCH_X86_REALMODE_H
> #define _ARCH_X86_REALMODE_H
>
> +/*
> + * Flag bit definitions for use with the flags field of the trampoline header
> + * when configured for X86_64

Let's use kernel nomenclature: "... of the trampoline header in the
CONFIG_X86_64 variant."

> + */
> +#define TH_FLAGS_SME_ENABLE_BIT 0
> +#define TH_FLAGS_SME_ENABLE BIT_ULL(TH_FLAGS_SME_ENABLE_BIT)

BIT() is the proper one for u32 flags variable.

> +
> +#ifndef __ASSEMBLY__
> +
> #include <linux/types.h>
> #include <asm/io.h>
>
> @@ -38,6 +47,7 @@ struct trampoline_header {
> u64 start;
> u64 efer;
> u32 cr4;
> + u32 flags;
> #endif
> };
>
> @@ -69,4 +79,6 @@ static inline size_t real_mode_size_needed(void)
> void set_real_mode_mem(phys_addr_t mem, size_t size);
> void reserve_real_mode(void);
>
> +#endif /* __ASSEMBLY__ */
> +
> #endif /* _ARCH_X86_REALMODE_H */
> diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
> index 44ed32a..a8e7ebe 100644
> --- a/arch/x86/realmode/init.c
> +++ b/arch/x86/realmode/init.c
> @@ -101,6 +101,10 @@ static void __init setup_real_mode(void)
> trampoline_cr4_features = &trampoline_header->cr4;
> *trampoline_cr4_features = mmu_cr4_features;
>
> + trampoline_header->flags = 0;
> + if (sme_me_mask)
> + trampoline_header->flags |= TH_FLAGS_SME_ENABLE;
> +
> trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
> trampoline_pgd[0] = trampoline_pgd_entry.pgd;
> trampoline_pgd[511] = init_level4_pgt[511].pgd;
> diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
> index dac7b20..94e29f4 100644
> --- a/arch/x86/realmode/rm/trampoline_64.S
> +++ b/arch/x86/realmode/rm/trampoline_64.S
> @@ -30,6 +30,7 @@
> #include <asm/msr.h>
> #include <asm/segment.h>
> #include <asm/processor-flags.h>
> +#include <asm/realmode.h>
> #include "realmode.h"
>
> .text
> @@ -92,6 +93,23 @@ ENTRY(startup_32)
> movl %edx, %fs
> movl %edx, %gs
>
> + /* Check for memory encryption support */
> + bt $TH_FLAGS_SME_ENABLE_BIT, pa_tr_flags
> + jnc .Ldone
> + movl $MSR_K8_SYSCFG, %ecx
> + rdmsr
> + bt $MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax
> + jc .Ldone
> +
> + /*
> + * Memory encryption is enabled but the MSR has not been set on this
> + * CPU so we can't continue

Can this ever happen?

I mean, we set TH_FLAGS_SME_ENABLE when sme_me_mask is set and this
would have happened only if the BSP has MSR_K8_SYSCFG[23] set.

How is it possible that that bit won't be set on some of the APs but set
on the BSP?

I'd assume the BIOS is doing a consistent setting everywhere...

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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