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    SubjectRe: [PATCH v5 32/32] x86/mm: Add support to make use of Secure Memory Encryption
    On Tue, Apr 18, 2017 at 04:22:23PM -0500, Tom Lendacky wrote:
    > Add support to check if SME has been enabled and if memory encryption
    > should be activated (checking of command line option based on the
    > configuration of the default state). If memory encryption is to be
    > activated, then the encryption mask is set and the kernel is encrypted
    > "in place."
    >
    > Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
    > ---
    > arch/x86/kernel/head_64.S | 1 +
    > arch/x86/mm/mem_encrypt.c | 83 +++++++++++++++++++++++++++++++++++++++++++--
    > 2 files changed, 80 insertions(+), 4 deletions(-)

    ...

    > +unsigned long __init sme_enable(struct boot_params *bp)
    > {
    > + const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
    > + unsigned int eax, ebx, ecx, edx;
    > + unsigned long me_mask;
    > + bool active_by_default;
    > + char buffer[16];
    > + u64 msr;
    > +
    > + /* Check for the SME support leaf */
    > + eax = 0x80000000;
    > + ecx = 0;
    > + native_cpuid(&eax, &ebx, &ecx, &edx);
    > + if (eax < 0x8000001f)
    > + goto out;
    > +
    > + /*
    > + * Check for the SME feature:
    > + * CPUID Fn8000_001F[EAX] - Bit 0
    > + * Secure Memory Encryption support
    > + * CPUID Fn8000_001F[EBX] - Bits 5:0
    > + * Pagetable bit position used to indicate encryption
    > + */
    > + eax = 0x8000001f;
    > + ecx = 0;
    > + native_cpuid(&eax, &ebx, &ecx, &edx);
    > + if (!(eax & 1))
    > + goto out;

    <---- newline here.

    > + me_mask = 1UL << (ebx & 0x3f);
    > +
    > + /* Check if SME is enabled */
    > + msr = __rdmsr(MSR_K8_SYSCFG);
    > + if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
    > + goto out;
    > +
    > + /*
    > + * Fixups have not been applied to phys_base yet, so we must obtain
    > + * the address to the SME command line option data in the following
    > + * way.
    > + */
    > + asm ("lea sme_cmdline_arg(%%rip), %0"
    > + : "=r" (cmdline_arg)
    > + : "p" (sme_cmdline_arg));
    > + asm ("lea sme_cmdline_on(%%rip), %0"
    > + : "=r" (cmdline_on)
    > + : "p" (sme_cmdline_on));
    > + asm ("lea sme_cmdline_off(%%rip), %0"
    > + : "=r" (cmdline_off)
    > + : "p" (sme_cmdline_off));
    > +
    > + if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
    > + active_by_default = true;
    > + else
    > + active_by_default = false;
    > +
    > + cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
    > + ((u64)bp->ext_cmd_line_ptr << 32));
    > +
    > + cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer));
    > +
    > + if (strncmp(buffer, cmdline_on, sizeof(buffer)) == 0)
    > + sme_me_mask = me_mask;

    Why doesn't simply

    if (!strncmp(buffer, "on", 2))
    ...

    work?

    --
    Regards/Gruss,
    Boris.

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

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