Re: [PATCH v8 01/40] x86/compressed/64: detect/setup SEV/SME features earlier in boot

Tom Lendacky
2021-12-15T14:43:29Z

On 12/14/21 6:14 PM, Venu Busireddy wrote:
> On 2021-12-14 20:10:16 +0100, Borislav Petkov wrote:
>> On Tue, Dec 14, 2021 at 11:46:14AM -0600, Venu Busireddy wrote:
>>> What I am suggesting should not have anything to do with the boot stage
>>> of the kernel.
>>
>> I know exactly what you're suggesting.
>>
>>> For example, both these functions call native_cpuid(), which is declared
>>> as an inline function. I am merely suggesting to do something similar
>>> to avoid the code duplication.
>>
>> Try it yourself. If you can come up with something halfway readable and
>> it builds, I'm willing to take a look.
>
> Patch (to be applied on top of sev-snp-v8 branch of
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FAMDESE%2Flinux.git&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Cbff83ee03b1147c39ea808d9bf5fe9d8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637751240978266883%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=D8t%2FwXY%2FYIl8aJXN%2BU7%2Flubln8AbhtdgB0f4DCNWp4w%3D&amp;reserved=0) is attached at the end.
>
> Here are a few things I did.
>
> 1. Moved all the common code that existed at the begining of
> sme_enable() and sev_enable() to an inline function named
> get_pagetable_bit_pos().
> 2. sme_enable() was using AMD_SME_BIT and AMD_SEV_BIT, whereas
> sev_enable() was dealing with raw bits. Moved those definitions to
> sev.h, and changed sev_enable() to use those definitions.
> 3. Make consistent use of BIT_ULL.
>
> Venu
>
>
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index c2bf99522e5e..b44d6b37796e 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -291,6 +291,7 @@ static void enforce_vmpl0(void)
> void sev_enable(struct boot_params *bp)
> {
> unsigned int eax, ebx, ecx, edx;
> + unsigned long pt_bit_pos; /* Pagetable bit position */
> bool snp;
>
> /*
> @@ -299,26 +300,8 @@ void sev_enable(struct boot_params *bp)
> */
> snp = snp_init(bp);
>
> - /* Check for the SME/SEV support leaf */
> - eax = 0x80000000;
> - ecx = 0;
> - native_cpuid(&eax, &ebx, &ecx, &edx);
> - if (eax < 0x8000001f)
> - return;
> -
> - /*
> - * Check for the SME/SEV feature:
> - * CPUID Fn8000_001F[EAX]
> - * - Bit 0 - Secure Memory Encryption support
> - * - Bit 1 - Secure Encrypted Virtualization 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);
> - /* Check whether SEV is supported */
> - if (!(eax & BIT(1))) {
> + /* Get the pagetable bit position if SEV is supported */
> + if ((get_pagetable_bit_pos(&pt_bit_pos, AMD_SEV_BIT)) < 0) {
> if (snp)
> error("SEV-SNP support indicated by CC blob, but not CPUID.");
> return;
> @@ -350,7 +333,7 @@ void sev_enable(struct boot_params *bp)
> if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
> error("SEV-SNP supported indicated by CC blob, but not SEV status MSR.");
>
> - sme_me_mask = BIT_ULL(ebx & 0x3f);
> + sme_me_mask = BIT_ULL(pt_bit_pos);
> }
>
> /* Search for Confidential Computing blob in the EFI config table. */
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 2c5f12ae7d04..41b096f28d02 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -224,6 +224,43 @@ static inline void native_cpuid(unsigned int *eax, unsigned int *ebx,
> : "memory");
> }
>
> +/*
> + * Returns the pagetable bit position in pt_bit_pos,
> + * iff the specified features are supported.
> + */
> +static inline int get_pagetable_bit_pos(unsigned long *pt_bit_pos,
> + unsigned long features)

I'm not a fan of this name. You are specifically returning the encryption
bit position but using a very generic name of get_pagetable_bit_pos() in a
very common header file. Maybe something more like get_me_bit() and move
the function to an existing SEV header file.

Also, this can probably just return an unsigned int that will be either 0
or the bit position, right? Then the check above can be for a zero value,
e.g.:

me_bit = get_me_bit();
if (!me_bit) {

...

sme_me_mask = BIT_ULL(me_bit);

That should work below, too, but you'll need to verify that.

> +{
> + unsigned int eax, ebx, ecx, edx;
> +
> + /* Check for the SME/SEV support leaf */
> + eax = 0x80000000;
> + ecx = 0;
> + native_cpuid(&eax, &ebx, &ecx, &edx);
> + if (eax < 0x8000001f)
> + return -1;

This can then be:

return 0;

> +
> + eax = 0x8000001f;
> + ecx = 0;
> + native_cpuid(&eax, &ebx, &ecx, &edx);
> +
> + /* Check whether the specified features are supported.
> + * SME/SEV features:
> + * CPUID Fn8000_001F[EAX]
> + * - Bit 0 - Secure Memory Encryption support
> + * - Bit 1 - Secure Encrypted Virtualization support
> + */
> + if (!(eax & features))
> + return -1;

and this can be:

return 0;

> +
> + /*
> + * CPUID Fn8000_001F[EBX]
> + * - Bits 5:0 - Pagetable bit position used to indicate encryption
> + */
> + *pt_bit_pos = (unsigned long)(ebx & 0x3f);

and this can be:

return ebx & 0x3f;

> + return 0;
> +}
> +
> #define native_cpuid_reg(reg) \
> static inline unsigned int native_cpuid_##reg(unsigned int op) \
> { \
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 7a5934af9d47..1a2344362ec6 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -17,6 +17,9 @@
> #define GHCB_PROTOCOL_MAX 2ULL
> #define GHCB_DEFAULT_USAGE 0ULL
>
> +#define AMD_SME_BIT BIT(0)
> +#define AMD_SEV_BIT BIT(1)
> +

Maybe this is where that new static inline function should go...

> #define VMGEXIT() { asm volatile("rep; vmmcall\n\r"); }
>
> enum es_result {
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index 2f723e106ed3..1ef50e969efd 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -508,38 +508,18 @@ void __init sme_enable(struct boot_params *bp)
> unsigned long feature_mask;
> bool active_by_default;
> unsigned long me_mask;
> + unsigned long pt_bit_pos; /* Pagetable bit position */

unsigned int and me_bit or me_bit_pos.

Thanks,
Tom

> char buffer[16];
> bool snp;
> u64 msr;
>
> snp = snp_init(bp);
>
> - /* Check for the SME/SEV support leaf */
> - eax = 0x80000000;
> - ecx = 0;
> - native_cpuid(&eax, &ebx, &ecx, &edx);
> - if (eax < 0x8000001f)
> + /* Get the pagetable bit position if SEV or SME are supported */
> + if ((get_pagetable_bit_pos(&pt_bit_pos, AMD_SEV_BIT | AMD_SME_BIT)) < 0)
> return;
>
> -#define AMD_SME_BIT BIT(0)
> -#define AMD_SEV_BIT BIT(1)
> -
> - /*
> - * Check for the SME/SEV feature:
> - * CPUID Fn8000_001F[EAX]
> - * - Bit 0 - Secure Memory Encryption support
> - * - Bit 1 - Secure Encrypted Virtualization 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);
> - /* Check whether SEV or SME is supported */
> - if (!(eax & (AMD_SEV_BIT | AMD_SME_BIT)))
> - return;
> -
> - me_mask = 1UL << (ebx & 0x3f);
> + me_mask = BIT_ULL(pt_bit_pos);
>
> /* Check the SEV MSR whether SEV or SME is enabled */
> sev_status = __rdmsr(MSR_AMD64_SEV);
>