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SubjectRe: [PATCH 2/3] x86/tme: Detect if TME and MKTME is activated by BIOS
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On Wed, 2018-01-31 at 12:15 +0300, Kirill A. Shutemov wrote:
> IA32_TME_ACTIVATE MSR (0x982) can be used to check if BIOS has
> enabled
> TME and MKTME. It includes which encryption policy/algorithm is
> selected
> for TME or available for MKTME. For MKTME, the MSR also enumerates
> how
> many KeyIDs are available.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> arch/x86/kernel/cpu/intel.c | 83
> +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 83 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/intel.c
> b/arch/x86/kernel/cpu/intel.c
> index 6936d14d4c77..5b95fa484837 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -517,6 +517,86 @@ static void detect_vmx_virtcap(struct
> cpuinfo_x86 *c)
> }
> }
>
> +#define MSR_IA32_TME_ACTIVATE 0x982

Should this MSR go into msr-index.h?

> +
> +#define TME_ACTIVATE_LOCKED(x) (x & 0x1)
> +#define TME_ACTIVATE_ENABLED(x) (x & 0x2)
> +
> +#define TME_ACTIVATE_POLICY(x) ((x >> 4) & 0xf)
> /* Bits 7:4 */
> +#define TME_ACTIVATE_POLICY_AES_XTS 0
> +
> +#define TME_ACTIVATE_KEYID_BITS(x) ((x >> 32) & 0xf) /
> * Bits 35:32 */
> +
> +#define TME_ACTIVATE_CRYPTO_ALGS(x) ((x >> 48) & 0xffff)
> /* Bits 63:48 */
> +#define TME_ACTIVATE_CRYPTO_AES_XTS 1
> +
> +#define MKTME_ENABLED 0
> +#define MKTME_DISABLED 1
> +#define MKTME_UNINITIALIZED 2
> +static int mktme_status = MKTME_UNINITIALIZED;
> +
> +static void detect_tme(struct cpuinfo_x86 *c)
> +{
> + u64 tme_activate, tme_policy, tme_crypto_algs;
> + int keyid_bits = 0, nr_keyids = 0;
> + static u64 tme_activate_cpu0 = 0;
> +
> + rdmsrl(MSR_IA32_TME_ACTIVATE, tme_activate);
> +
> + if (mktme_status != MKTME_UNINITIALIZED) {
> + /* Broken BIOS? */
> + if (tme_activate != tme_activate_cpu0) {
> + pr_err_once("TME: configuation is
> inconsistent between CPUs\n");
> + mktme_status = MKTME_DISABLED;
> + }
> + goto out;

Why goto out here? If something goes wrong, I think it is pointless to
read keyID bits staff? IMHO if something goes wrong, you should set
mktme_status to disabled, and clear tme_activate_cpu0?

> + }
> +
> + tme_activate_cpu0 = tme_activate;
> +
> + if (!TME_ACTIVATE_LOCKED(tme_activate) ||
> !TME_ACTIVATE_ENABLED(tme_activate)) {
> + pr_info("TME: not enabled by BIOS\n");
> + mktme_status = MKTME_DISABLED;
> + goto out;

I think it is pointless to read keyID bits staff if TME is not even
enabled.

> + }
> +
> + pr_info("TME: enabled by BIOS\n");
> +
> + tme_policy = TME_ACTIVATE_POLICY(tme_activate);
> + if (tme_policy != TME_ACTIVATE_POLICY_AES_XTS)
> + pr_warn("TME: Unknown policy is active: %#llx\n",
> tme_policy);
> +
> + tme_crypto_algs = TME_ACTIVATE_CRYPTO_ALGS(tme_activate);
> + if (!(tme_crypto_algs & TME_ACTIVATE_CRYPTO_AES_XTS)) {
> + pr_err("MKTME: No known encryption algorithm is
> supported: %#llx\n",
> + tme_crypto_algs);
> + mktme_status = MKTME_DISABLED;
> + }

To me it is a little bit confusing about the naming. tme_policy is the
crypto_alg used by TME keyID (0), and tme_crypto_algs is bitmap of
supported crypto_algs for MK-TME. Probably a better naming is needed?
And the naming of TME_ACTIVATE_POLICY(x), TME_ACTIVATE_CRYPTO_ALGS(x)
above as well?

> +out:
> + keyid_bits = TME_ACTIVATE_KEYID_BITS(tme_activate);
> + nr_keyids = (1UL << keyid_bits) - 1;
> + if (nr_keyids) {
> + pr_info_once("MKTME: enabled by BIOS\n");
> + pr_info_once("MKTME: %d KeyIDs available\n",
> nr_keyids);
> + } else {
> + pr_info_once("MKTME: disabled by BIOS\n");
> + }
> +
> + if (mktme_status == MKTME_UNINITIALIZED) {
> + /* MKTME is usable */
> + mktme_status = MKTME_ENABLED;
> + }
> +
> + /*
> + * Exclude KeyID bits from physical address bits.
> + *
> + * We have to do this even if we are not going to use KeyID
> bits
> + * ourself. VM guests still have to know that these bits are
> not usable
> + * for physical address.
> + */
Currently KVM uses CPUID to get such info directly, but not consulting
c->x86_phys_bits. I think it may be reasonable for KVM to consulting c-
>x86_phys_bits for MK-TME, but IMHO the real reason we need to do this
is this is just the fact, and c->x86_phys_bits needs to reflect the
fact, so probably the comments can be refined.

Thanks,
-Kai

> + c->x86_phys_bits -= keyid_bits;
> +}
> +
> static void init_intel_energy_perf(struct cpuinfo_x86 *c)
> {
> u64 epb;
> @@ -687,6 +767,9 @@ static void init_intel(struct cpuinfo_x86 *c)
> if (cpu_has(c, X86_FEATURE_VMX))
> detect_vmx_virtcap(c);
>
> + if (cpu_has(c, X86_FEATURE_TME))
> + detect_tme(c);
> +
> init_intel_energy_perf(c);
>
> init_intel_misc_features(c);

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