linux-kernel - Re: [PATCH v4 07/15] x86/sev: Use the SVSM to create a vCPU when not in VMPL0

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Date: Mon, 27 May 2024 14:33:24 +0200
From: Borislav Petkov <bp@...en8.de>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-coco@...ts.linux.dev, svsm-devel@...onut-svsm.dev,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Michael Roth <michael.roth@....com>,
	Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v4 07/15] x86/sev: Use the SVSM to create a vCPU when not
 in VMPL0

On Wed, Apr 24, 2024 at 10:58:03AM -0500, Tom Lendacky wrote:
> -static int snp_set_vmsa(void *va, bool vmsa)
> +static int base_snp_set_vmsa(void *va, bool vmsa)

s/base_/__/

The svsm_-prefixed ones are already a good enough distinction...

>  {
>  	u64 attrs;
>  
> @@ -1013,6 +1013,40 @@ static int snp_set_vmsa(void *va, bool vmsa)
>  	return rmpadjust((unsigned long)va, RMP_PG_SIZE_4K, attrs);
>  }
>  
> +static int svsm_snp_set_vmsa(void *va, void *caa, int apic_id, bool vmsa)
								  ^^^^^^^^^^^

bool create_vmsa or so, to denote what this arg means.

> +{
> +	struct svsm_call call = {};
> +	unsigned long flags;
> +	int ret;
> +
> +	local_irq_save(flags);
> +
> +	call.caa = this_cpu_read(svsm_caa);
> +	call.rcx = __pa(va);
> +
> +	if (vmsa) {
> +		/* Protocol 0, Call ID 2 */
> +		call.rax = SVSM_CORE_CALL(SVSM_CORE_CREATE_VCPU);
> +		call.rdx = __pa(caa);
> +		call.r8  = apic_id;
> +	} else {
> +		/* Protocol 0, Call ID 3 */
> +		call.rax = SVSM_CORE_CALL(SVSM_CORE_DELETE_VCPU);
> +	}
> +
> +	ret = svsm_protocol(&call);
> +
> +	local_irq_restore(flags);
> +
> +	return ret;
> +}
> +
> +static int snp_set_vmsa(void *va, void *caa, int apic_id, bool vmsa)
> +{
> +	return vmpl ? svsm_snp_set_vmsa(va, caa, apic_id, vmsa)
> +		    : base_snp_set_vmsa(va, vmsa);

Why do you even need helpers if you're not going to use them somewhere
else? Just put the whole logic inside snp_set_vmsa().

> +}
> +
>  #define __ATTR_BASE		(SVM_SELECTOR_P_MASK | SVM_SELECTOR_S_MASK)
>  #define INIT_CS_ATTRIBS		(__ATTR_BASE | SVM_SELECTOR_READ_MASK | SVM_SELECTOR_CODE_MASK)
>  #define INIT_DS_ATTRIBS		(__ATTR_BASE | SVM_SELECTOR_WRITE_MASK)
> @@ -1044,11 +1078,11 @@ static void *snp_alloc_vmsa_page(int cpu)
>  	return page_address(p + 1);
>  }
>  
> -static void snp_cleanup_vmsa(struct sev_es_save_area *vmsa)
> +static void snp_cleanup_vmsa(struct sev_es_save_area *vmsa, int apic_id)
>  {
>  	int err;
>  
> -	err = snp_set_vmsa(vmsa, false);
> +	err = snp_set_vmsa(vmsa, NULL, apic_id, false);
>  	if (err)
>  		pr_err("clear VMSA page failed (%u), leaking page\n", err);
>  	else
> @@ -1059,6 +1093,7 @@ static int wakeup_cpu_via_vmgexit(u32 apic_id, unsigned long start_ip)
>  {
>  	struct sev_es_save_area *cur_vmsa, *vmsa;
>  	struct ghcb_state state;
> +	struct svsm_ca *caa;
>  	unsigned long flags;
>  	struct ghcb *ghcb;
>  	u8 sipi_vector;
> @@ -1105,6 +1140,12 @@ static int wakeup_cpu_via_vmgexit(u32 apic_id, unsigned long start_ip)
>  	if (!vmsa)
>  		return -ENOMEM;
>  
> +	/*
> +	 * If an SVSM is present, then the SVSM CAA per-CPU variable will
> +	 * have a value, otherwise it will be NULL.
> +	 */

	/* If an SVSM is present, the SVSM per-CPU CAA will be !NULL. */

Shorter.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette