linux-kernel - Re: [RFC v2-fix-v2 1/1] x86: Introduce generic protected guest abstractionn

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Date:   Mon, 7 Jun 2021 22:55:44 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [RFC v2-fix-v2 1/1] x86: Introduce generic protected guest
 abstractionn

On Thu, Jun 03, 2021 at 08:15:46PM +0200, Borislav Petkov wrote:
> From f1e9f051c86b09fe660f49b0307bc7c6cec5e6f4 Mon Sep 17 00:00:00 2001
> From: Borislav Petkov <bp@...e.de>
> Date: Thu, 3 Jun 2021 20:03:31 +0200
> Subject: Convert sme_active()
> 
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 9c80c68d75b5..1bb9f22629fc 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -50,7 +50,6 @@ void __init mem_encrypt_free_decrypted_mem(void);
>  void __init mem_encrypt_init(void);
>  
>  void __init sev_es_init_vc_handling(void);
> -bool sme_active(void);
>  bool sev_active(void);
>  bool sev_es_active(void);
>  
> @@ -75,7 +74,6 @@ static inline void __init sme_encrypt_kernel(struct boot_params *bp) { }
>  static inline void __init sme_enable(struct boot_params *bp) { }
>  
>  static inline void sev_es_init_vc_handling(void) { }
> -static inline bool sme_active(void) { return false; }
>  static inline bool sev_active(void) { return false; }
>  static inline bool sev_es_active(void) { return false; }
>  
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index c078b0d3ab0e..1d88232146ab 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -387,7 +387,7 @@ void machine_kexec(struct kimage *image)
>  				       (unsigned long)page_list,
>  				       image->start,
>  				       image->preserve_context,
> -				       sme_active());
> +				       protected_guest_has(VM_HOST_MEM_ENCRYPT));
>  
>  #ifdef CONFIG_KEXEC_JUMP
>  	if (image->preserve_context)

I think conversions like this are wrong: relocate_kernel(), which got
called here, only knows how to deal with SME, not how to handle some
generic case.

(After a quick check, looks like all conversions in the patch are wrong
for the same reason.)

If code is written to handle a specific technology we need to stick with
a check that makes it clear. Trying to make sound generic only leads to
confusion.

Also, we have host memory encryption that doesn't require any of this
code: TME makes the ectryption transparently to OS.

Maybe it's better to take a conservative path: keep a check specific until
we find it can serve more than one HW feature?

-- 
 Kirill A. Shutemov