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Date: Tue, 11 Jul 2017 10:12:41 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-arch <linux-arch@...r.kernel.org>, linux-efi@...r.kernel.org,
kvm@...r.kernel.org, linux-doc@...r.kernel.org,
the arch/x86 maintainers <x86@...nel.org>,
kexec@...ts.infradead.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
kasan-dev@...glegroups.com, xen-devel@...ts.xen.org,
Linux-MM <linux-mm@...ck.org>, iommu@...ts.linux-foundation.org,
Brijesh Singh <brijesh.singh@....com>,
Toshimitsu Kani <toshi.kani@....com>,
Radim Krčmář <rkrcmar@...hat.com>,
Matt Fleming <matt@...eblueprint.co.uk>,
Alexander Potapenko <glider@...gle.com>,
"H. Peter Anvin" <hpa@...or.com>,
Larry Woodman <lwoodman@...hat.com>,
Jonathan Corbet <corbet@....net>,
Joerg Roedel <joro@...tes.org>,
"Michael S. Tsirkin" <mst@...hat.com>,
Ingo Molnar <mingo@...hat.com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Dave Young <dyoung@...hat.com>, Rik van Riel <riel@...hat.com>,
Arnd Bergmann <arnd@...db.de>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Borislav Petkov <bp@...en8.de>,
Andy Lutomirski <luto@...nel.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Juergen Gross <jgross@...e.com>,
Thomas Gleixner <tglx@...utronix.de>,
Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v9 04/38] x86/CPU/AMD: Add the Secure Memory Encryption
CPU feature
On 7/11/2017 12:07 AM, Brian Gerst wrote:
> On Mon, Jul 10, 2017 at 3:41 PM, Tom Lendacky <thomas.lendacky@....com> wrote:
>> On 7/8/2017 7:50 AM, Brian Gerst wrote:
>>>
>>> On Fri, Jul 7, 2017 at 9:38 AM, Tom Lendacky <thomas.lendacky@....com>
>>> wrote:
>>>>
>>>> Update the CPU features to include identifying and reporting on the
>>>> Secure Memory Encryption (SME) feature. SME is identified by CPUID
>>>> 0x8000001f, but requires BIOS support to enable it (set bit 23 of
>>>> MSR_K8_SYSCFG). Only show the SME feature as available if reported by
>>>> CPUID and enabled by BIOS.
>>>>
>>>> Reviewed-by: Borislav Petkov <bp@...e.de>
>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>>>> ---
>>>> arch/x86/include/asm/cpufeatures.h | 1 +
>>>> arch/x86/include/asm/msr-index.h | 2 ++
>>>> arch/x86/kernel/cpu/amd.c | 13 +++++++++++++
>>>> arch/x86/kernel/cpu/scattered.c | 1 +
>>>> 4 files changed, 17 insertions(+)
>>>>
>>>> diff --git a/arch/x86/include/asm/cpufeatures.h
>>>> b/arch/x86/include/asm/cpufeatures.h
>>>> index 2701e5f..2b692df 100644
>>>> --- a/arch/x86/include/asm/cpufeatures.h
>>>> +++ b/arch/x86/include/asm/cpufeatures.h
>>>> @@ -196,6 +196,7 @@
>>>>
>>>> #define X86_FEATURE_HW_PSTATE ( 7*32+ 8) /* AMD HW-PState */
>>>> #define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD
>>>> ProcFeedbackInterface */
>>>> +#define X86_FEATURE_SME ( 7*32+10) /* AMD Secure Memory
>>>> Encryption */
>>>
>>>
>>> Given that this feature is available only in long mode, this should be
>>> added to disabled-features.h as disabled for 32-bit builds.
>>
>>
>> I can add that. If the series needs a re-spin then I'll include this
>> change in the series, otherwise I can send a follow-on patch to handle
>> the feature for 32-bit builds if that works.
>>
>>
>>>
>>>> #define X86_FEATURE_INTEL_PPIN ( 7*32+14) /* Intel Processor Inventory
>>>> Number */
>>>> #define X86_FEATURE_INTEL_PT ( 7*32+15) /* Intel Processor Trace */
>>>> diff --git a/arch/x86/include/asm/msr-index.h
>>>> b/arch/x86/include/asm/msr-index.h
>>>> index 18b1623..460ac01 100644
>>>> --- a/arch/x86/include/asm/msr-index.h
>>>> +++ b/arch/x86/include/asm/msr-index.h
>>>> @@ -352,6 +352,8 @@
>>>> #define MSR_K8_TOP_MEM1 0xc001001a
>>>> #define MSR_K8_TOP_MEM2 0xc001001d
>>>> #define MSR_K8_SYSCFG 0xc0010010
>>>> +#define MSR_K8_SYSCFG_MEM_ENCRYPT_BIT 23
>>>> +#define MSR_K8_SYSCFG_MEM_ENCRYPT
>>>> BIT_ULL(MSR_K8_SYSCFG_MEM_ENCRYPT_BIT)
>>>> #define MSR_K8_INT_PENDING_MSG 0xc0010055
>>>> /* C1E active bits in int pending message */
>>>> #define K8_INTP_C1E_ACTIVE_MASK 0x18000000
>>>> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
>>>> index bb5abe8..c47ceee 100644
>>>> --- a/arch/x86/kernel/cpu/amd.c
>>>> +++ b/arch/x86/kernel/cpu/amd.c
>>>> @@ -611,6 +611,19 @@ static void early_init_amd(struct cpuinfo_x86 *c)
>>>> */
>>>> if (cpu_has_amd_erratum(c, amd_erratum_400))
>>>> set_cpu_bug(c, X86_BUG_AMD_E400);
>>>> +
>>>> + /*
>>>> + * BIOS support is required for SME. If BIOS has not enabled SME
>>>> + * then don't advertise the feature (set in scattered.c)
>>>> + */
>>>> + if (cpu_has(c, X86_FEATURE_SME)) {
>>>> + u64 msr;
>>>> +
>>>> + /* Check if SME is enabled */
>>>> + rdmsrl(MSR_K8_SYSCFG, msr);
>>>> + if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
>>>> + clear_cpu_cap(c, X86_FEATURE_SME);
>>>> + }
>>>
>>>
>>> This should be conditional on CONFIG_X86_64.
>>
>>
>> If I make the scattered feature support conditional on CONFIG_X86_64
>> (based on comment below) then cpu_has() will always be false unless
>> CONFIG_X86_64 is enabled. So this won't need to be wrapped by the
>> #ifdef.
>
> If you change it to use cpu_feature_enabled(), gcc will see that it is
> disabled and eliminate the dead code at compile time.
>
>>>
>>>> }
>>>>
>>>> static void init_amd_k8(struct cpuinfo_x86 *c)
>>>> diff --git a/arch/x86/kernel/cpu/scattered.c
>>>> b/arch/x86/kernel/cpu/scattered.c
>>>> index 23c2350..05459ad 100644
>>>> --- a/arch/x86/kernel/cpu/scattered.c
>>>> +++ b/arch/x86/kernel/cpu/scattered.c
>>>> @@ -31,6 +31,7 @@ struct cpuid_bit {
>>>> { X86_FEATURE_HW_PSTATE, CPUID_EDX, 7, 0x80000007, 0 },
>>>> { X86_FEATURE_CPB, CPUID_EDX, 9, 0x80000007, 0 },
>>>> { X86_FEATURE_PROC_FEEDBACK, CPUID_EDX, 11, 0x80000007, 0 },
>>>> + { X86_FEATURE_SME, CPUID_EAX, 0, 0x8000001f, 0 },
>>>
>>>
>>> This should also be conditional. We don't want to set this feature on
>>> 32-bit, even if the processor has support.
>>
>>
>> Can do. See comment above about re-spin vs. follow-on patch.
>>
>> Thanks,
>> Tom
>
> A followup patch will be OK if there is no code that will get confused
> by the SME bit being present but not active.
The feature bit is mainly there for /proc/cpuinfo. The code uses
sme_active() in order to determine how to behave. Under CONFIG_X86_32,
sme_active() is always 0.
Based on the comment related to patch 7 (ioremap() of ISA range) I may
need to re-spin the patchset. I'll include this change following
the recommendation from Boris to use the IS_ENABLED(CONFIG_X86_32) check
to clear the feature bit.
Thanks,
Tom
>
> --
> Brian Gerst
>
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