linux-kernel - Re: [PATCH v3 01/21] x86/virt/tdx: Detect SEAM

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Date:   Mon, 18 Apr 2022 15:29:36 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, dave.hansen@...el.com,
        len.brown@...el.com, tony.luck@...el.com,
        rafael.j.wysocki@...el.com, reinette.chatre@...el.com,
        dan.j.williams@...el.com, peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com, isaku.yamahata@...el.com
Subject: Re: [PATCH v3 01/21] x86/virt/tdx: Detect SEAM



On 4/5/22 9:49 PM, Kai Huang wrote:
> +/* BIOS must configure SEAMRR registers for all cores consistently */
> +static u64 seamrr_base, seamrr_mask;
> +
> +static bool __seamrr_enabled(void)
> +{
> +	return (seamrr_mask & SEAMRR_ENABLED_BITS) == SEAMRR_ENABLED_BITS;
> +}
> +
> +static void detect_seam_bsp(struct cpuinfo_x86 *c)
> +{
> +	u64 mtrrcap, base, mask;
> +
> +	/* SEAMRR is reported via MTRRcap */
> +	if (!boot_cpu_has(X86_FEATURE_MTRR))
> +		return;
> +
> +	rdmsrl(MSR_MTRRcap, mtrrcap);
> +	if (!(mtrrcap & MTRR_CAP_SEAMRR))
> +		return;
> +
> +	rdmsrl(MSR_IA32_SEAMRR_PHYS_BASE, base);
> +	if (!(base & SEAMRR_PHYS_BASE_CONFIGURED)) {
> +		pr_info("SEAMRR base is not configured by BIOS\n");
> +		return;
> +	}
> +
> +	rdmsrl(MSR_IA32_SEAMRR_PHYS_MASK, mask);
> +	if ((mask & SEAMRR_ENABLED_BITS) != SEAMRR_ENABLED_BITS) {
> +		pr_info("SEAMRR is not enabled by BIOS\n");
> +		return;
> +	}
> +
> +	seamrr_base = base;
> +	seamrr_mask = mask;
> +}
> +
> +static void detect_seam_ap(struct cpuinfo_x86 *c)
> +{
> +	u64 base, mask;
> +
> +	/*
> +	 * Don't bother to detect this AP if SEAMRR is not
> +	 * enabled after earlier detections.
> +	 */
> +	if (!__seamrr_enabled())
> +		return;
> +
> +	rdmsrl(MSR_IA32_SEAMRR_PHYS_BASE, base);
> +	rdmsrl(MSR_IA32_SEAMRR_PHYS_MASK, mask);
> +
> +	if (base == seamrr_base && mask == seamrr_mask)
> +		return;
> +
> +	pr_err("Inconsistent SEAMRR configuration by BIOS\n");

Do we need to panic for SEAM config issue (for security)?

> +	/* Mark SEAMRR as disabled. */
> +	seamrr_base = 0;
> +	seamrr_mask = 0
> +}
> +
> +static void detect_seam(struct cpuinfo_x86 *c)
> +{

why not do this check directly in tdx_detect_cpu()?

> +	if (c == &boot_cpu_data)
> +		detect_seam_bsp(c);
> +	else
> +		detect_seam_ap(c);
> +}
> +
> +void tdx_detect_cpu(struct cpuinfo_x86 *c)
> +{
> +	detect_seam(c);
> +}

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer