linux-kernel - Re: [PATCH v13 00/11] Parallel CPU bringup for x86

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Date:   Tue, 7 Mar 2023 10:45:59 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Usama Arif <usama.arif@...edance.com>, tglx@...utronix.de,
        kim.phillips@....com, brgerst@...il.com
Cc:     piotrgorski@...hyos.org, oleksandr@...alenko.name,
        arjan@...ux.intel.com, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, x86@...nel.org,
        pbonzini@...hat.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        seanjc@...gle.com, pmenzel@...gen.mpg.de, fam.zheng@...edance.com,
        punit.agrawal@...edance.com, simon.evans@...edance.com,
        liangma@...ngbit.com
Subject: Re: [PATCH v13 00/11] Parallel CPU bringup for x86_64

On 3/7/23 08:42, David Woodhouse wrote:
> On Thu, 2023-03-02 at 11:12 +0000, Usama Arif wrote:
>> The main code change over v12 is to fix the build error when
>> CONFIG_FORCE_NR_CPUS is present.
>>
>> The commit message for removing initial stack has also been improved, typos
>> have been fixed and extra comments have been added to make code clearer.
> 
> Might something like this make it work in parallel with SEV-SNP? If so,
> I can clean it up and adjust the C code to actually invoke it...

This should be ok for both SEV-ES and SEV-SNP.

> 
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index b8357d6ecd47..f25df4bd318e 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -70,6 +70,7 @@
>   	/* GHCBData[63:12] */				\
>   	(((u64)(v) & GENMASK_ULL(63, 12)) >> 12)
>   
> +#ifndef __ASSEMBLY__
>   /*
>    * SNP Page State Change Operation
>    *
> @@ -160,6 +161,8 @@ struct snp_psc_desc {
>   
>   #define GHCB_RESP_CODE(v)		((v) & GHCB_MSR_INFO_MASK)
>   
> +#endif /* __ASSEMBLY__ */
> +
>   /*
>    * Error codes related to GHCB input that can be communicated back to the guest
>    * by setting the lower 32-bits of the GHCB SW_EXITINFO1 field to 2.
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index defe76ee9e64..0c26f80f488c 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -204,6 +204,7 @@ extern unsigned int smpboot_control;
>   /* Control bits for startup_64 */
>   #define STARTUP_APICID_CPUID_0B	0x80000000
>   #define STARTUP_APICID_CPUID_01	0x40000000
> +#define STARTUP_APICID_SEV_SNP	0x20000000
>   
>   #define STARTUP_PARALLEL_MASK (STARTUP_APICID_CPUID_01 | STARTUP_APICID_CPUID_0B)
>   
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index c35f7c173832..b2571034562c 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -26,7 +26,7 @@
>   #include <asm/nospec-branch.h>
>   #include <asm/fixmap.h>
>   #include <asm/smp.h>
> -
> +#include <asm/sev-common.h>
>   /*
>    * We are not able to switch in one step to the final KERNEL ADDRESS SPACE
>    * because we need identity-mapped pages.
> @@ -242,6 +242,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
>   	 *
>   	 * Bit 31	STARTUP_APICID_CPUID_0B flag (use CPUID 0x0b)
>   	 * Bit 30	STARTUP_APICID_CPUID_01 flag (use CPUID 0x01)
> +	 * Bit 29	STARTUP_APICID_SEV_SNP flag (CPUID 0x0v via GHCB MSR)
>   	 * Bit 0-24	CPU# if STARTUP_APICID_CPUID_xx flags are not set
>   	 */
>   	movl	smpboot_control(%rip), %ecx
> @@ -249,6 +250,8 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
>   	jnz	.Luse_cpuid_0b
>   	testl	$STARTUP_APICID_CPUID_01, %ecx
>   	jnz	.Luse_cpuid_01
> +	testl	$STARTUP_APICID_SEV_SNP, %ecx
> +	jnz	.Luse_sev_cpuid_0b
>   	andl	$0x0FFFFFFF, %ecx
>   	jmp	.Lsetup_cpu
>   
> @@ -259,6 +262,18 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
>   	shr	$24, %edx
>   	jmp	.Lsetup_AP
>   
> +.Luse_sev_cpuid_0b:
> +	movl	$MSR_AMD64_SEV_ES_GHCB, %ecx
> +	# GHCB_CPUID_REQ(0x0b, GHCB_CPUID_REQ_EDX)
> +	movq	$0xc00000040000000b, %rax
> +	xorl	%edx, %edx
> +	vmgexit

According to the GHCB spec, the GHCB MSR protocol is triggered when the 
GHCB value is non-zero in bits 11:0. For the CPUID function, bits 63:32 
hold the CPUID function, bits 31:30 hold the requested register and bits 
11:0 == 0x4. So this should be:

	/* Set the GHCB MSR to request CPUID 0xB_EDX */
	movl	$MSR_AMD64_SEV_ES_GHCB, %ecx
	movl	$0xc0000004, %eax
	movl	$0xb, %edx
	wrmsr

	/* Perform GHCB MSR protocol */
	vmgexit

	/*
	 * Get the result. After the RDMSR:
	 *   EAX should be 0xc0000005
	 *   EDX should have the CPUID register value and since EDX
	 *   is the target register, no need to move the result.
	 */
> +	rdmsr
> +	andl	$GHCB_MSR_INFO_MASK, %eax
> +	cmpl	$GHCB_MSR_CPUID_RESP, %eax
> +	jne	1f
> +	jmp	.Lsetup_AP
> +
>   .Luse_cpuid_0b:
>   	mov	$0x0B, %eax
>   	xorl	%ecx, %ecx
> 

Thanks,
Tom

>