linux-kernel - Re: [PATCH v2 2/8] x86/mtrr: support setting MTRR state for software defined MTRRs

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Message-ID: <01fa7eb8-e534-1c67-3629-7834e7df3c5d@suse.com>
Date:   Tue, 14 Feb 2023 08:01:56 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        lists@...dbynature.de, mikelley@...rosoft.com,
        torvalds@...ux-foundation.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 2/8] x86/mtrr: support setting MTRR state for software
 defined MTRRs

On 13.02.23 19:43, Borislav Petkov wrote:
> On Mon, Feb 13, 2023 at 04:36:12PM +0100, Juergen Gross wrote:
>> In the end I wouldn't mind dropping the fixed MTRRs from the interface, as
>> they are currently not needed at all.
> 
> Yes, the less the better.
> 
>> I'd say we go with what is needed right now. And having a single interface
>> makes all the sanity checking you are asking for easier.
> 
> I guess I need to remember to finish designing this if more users
> appear...
> 
>> What are you especially asking for?
>>
>> With my current patches Xen PV dom0 will call mtrr_overwrite_state() before
>> x86_hyper_type is set, while a Hyper-V SEV-SNP guest will make the call after
>> it has been set. Both calls happen before cache_bp_init().
>>
>> So I could move the mtrr_overwrite_state() call for Xen PV dom0 into its
>> init_platform() callback and check in mtrr_overwrite_state() x86_hyper_type
>> to be set,
> 
> I believe that is good enough, see below.
> 
>> or I could reject a call of mtrr_overwrite_state() after the call of
>> cache_bp_init() has happened, or I could do both.
> 
> I think one thing is enough as we'll be loud enough.
> 
> ---
> diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
> index b73fe243c7fd..2dbe2c10e959 100644
> --- a/arch/x86/kernel/cpu/mtrr/mtrr.c
> +++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
> @@ -49,6 +49,7 @@
>   #include <asm/cacheinfo.h>
>   #include <asm/cpufeature.h>
>   #include <asm/e820/api.h>
> +#include <asm/hypervisor.h>
>   #include <asm/mtrr.h>
>   #include <asm/msr.h>
>   #include <asm/memtype.h>
> @@ -668,7 +669,12 @@ void __init mtrr_bp_init(void)
>   	const char *why = "(not available)";
>   	unsigned int phys_addr;
>   
> +#ifdef CONFIG_HYPERVISOR_GUEST
>   	if (mtrr_state.enabled) {
> +
> +		/* This should not happen without a hypervisor present. */
> +		WARN_ON_ONCE(!x86_hyper_type);
> +
>   		/* Software overwrite of MTRR state, only for generic case. */
>   		mtrr_calc_physbits(true);
>   		init_table();
> @@ -676,6 +682,7 @@ void __init mtrr_bp_init(void)
>   
>   		return;
>   	}
> +#endif

I will change this a little bit in order to avoid the #ifdef by using
"WARN_ON(hypervisor_is_type() == X86_HYPER_NATIVE);"


Juergen

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