linux-kernel - Re: [PATCH v5 04/15] x86/mtrr: support setting MTRR state for software defined MTRRs

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Date:   Mon, 3 Apr 2023 02:25:40 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Gross, Jurgen" <jgross@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "mikelley@...rosoft.com" <mikelley@...rosoft.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v5 04/15] x86/mtrr: support setting MTRR state for
 software defined MTRRs

On Sat, 2023-04-01 at 08:36 +0200, Juergen Gross wrote:
> +/**
> + * mtrr_overwrite_state - set static MTRR state
> + *
> + * Used to set MTRR state via different means (e.g. with data obtained from
> + * a hypervisor).
> + * Is allowed only for special cases when running virtualized. Must be called
> + * from the x86_init.hyper.init_platform() hook.
> + */
> +void mtrr_overwrite_state(struct mtrr_var_range *var, unsigned int num_var,
> +			  mtrr_type def_type)
> +{
> +	unsigned int i;
> +
> +	/* Only allowed to be called once before mtrr_bp_init(). */
> +	if (WARN_ON(mtrr_state_set))
> +		return;
> +
> +	/* Only allowed when running virtualized. */
> +	if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR))
> +		return;
> +
> +	/*
> +	 * Only allowed for special virtualization cases:
> +	 * - when running as SEV-SNP guest
> +	 * - when running as Hyper-V isolated guest
> +	 * - when running as Xen PV guest
> +	 * - when running as TSX guest
			     ^
			     TDX guest

> +	 */
> +	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP) &&
> +	    !hv_is_isolation_supported() &&
> +	    !cpu_feature_enabled(X86_FEATURE_XENPV) &&
> +	    !cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
> +		return;
> +
> +	/* Disable MTRR in order to disable MTRR modifications. */
> +	setup_clear_cpu_cap(X86_FEATURE_MTRR);
> +
> +	if (var) {
> +		if (num_var > MTRR_MAX_VAR_RANGES) {
> +			pr_warn("Trying to overwrite MTRR state with %u variable entries\n",
> +				num_var);
> +			num_var = MTRR_MAX_VAR_RANGES;
> +		}
> +		for (i = 0; i < num_var; i++)
> +			mtrr_state.var_ranges[i] = var[i];
> +		num_var_ranges = num_var;
> +	}
> +
> +	mtrr_state.def_type = def_type;
> +	mtrr_state.enabled |= MTRR_STATE_MTRR_ENABLED;
> +
> +	mtrr_state_set = 1;
> +}
> +
>  /**
>   * mtrr_type_lookup - look up memory type in MTRR
>   *
> diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
> index 1beb38f7a7a3..1c19d67ddab3 100644
> --- a/arch/x86/kernel/cpu/mtrr/mtrr.c
> +++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
> @@ -666,6 +666,15 @@ void __init mtrr_bp_init(void)
>  	const char *why = "(not available)";
>  	unsigned int phys_addr;
>  
> +	if (!generic_mtrrs && mtrr_state.enabled) {
> +		/* Software overwrite of MTRR state, only for generic case. */
							      ^
							      !generic case?

> +		mtrr_calc_physbits(true);
> +		init_table();
> +		pr_info("MTRRs set to read-only\n");
> +
> +		return;
> +	}
> +
>  	phys_addr = mtrr_calc_physbits(generic_mtrrs);