Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1671420 > unrolled thread

Re: [PATCH v7 08/36] x86/mm: Add support to enable SME in early boot processing

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [PATCH v7 08/36] x86/mm: Add support to enable SME in early boot  processing Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 09:20 +0200
    Re: [PATCH v7 08/36] x86/mm: Add support to enable SME in early boot  processing Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 18:40 +0200
      Re: [PATCH v7 08/36] x86/mm: Add support to enable SME in early boot  processing Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 21:00 +0200

#1671420 — Re: [PATCH v7 08/36] x86/mm: Add support to enable SME in early boot processing

On Fri, 16 Jun 2017, Tom Lendacky wrote:
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index a105796..988b336 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -15,16 +15,24 @@
>  
>  #ifndef __ASSEMBLY__
>  
> +#include <linux/init.h>
> +
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  
>  extern unsigned long sme_me_mask;
>  
> +void __init sme_enable(void);
> +
>  #else	/* !CONFIG_AMD_MEM_ENCRYPT */
>  
>  #define sme_me_mask	0UL
>  
> +static inline void __init sme_enable(void) { }
> +
>  #endif	/* CONFIG_AMD_MEM_ENCRYPT */
>  
> +unsigned long sme_get_me_mask(void);

Why is this an unconditional function? Isn't the mask simply 0 when the MEM
ENCRYPT support is disabled?

> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 6225550..ef12729 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -78,7 +78,29 @@ startup_64:
>  	call	__startup_64
>  	popq	%rsi
>  
> -	movq	$(early_top_pgt - __START_KERNEL_map), %rax
> +	/*
> +	 * Encrypt the kernel if SME is active.
> +	 * The real_mode_data address is in %rsi and that register can be
> +	 * clobbered by the called function so be sure to save it.
> +	 */
> +	push	%rsi
> +	call	sme_encrypt_kernel
> +	pop	%rsi

That does not make any sense. Neither the call to sme_encrypt_kernel() nor
the following call to sme_get_me_mask().

__startup_64() is already C code, so why can't you simply call that from
__startup_64() in C and return the mask from there?

> @@ -98,7 +120,20 @@ ENTRY(secondary_startup_64)
>  	/* Sanitize CPU configuration */
>  	call verify_cpu
>  
> -	movq	$(init_top_pgt - __START_KERNEL_map), %rax
> +	/*
> +	 * Get the SME encryption mask.
> +	 *  The encryption mask will be returned in %rax so we do an ADD
> +	 *  below to be sure that the encryption mask is part of the
> +	 *  value that will stored in %cr3.
> +	 *
> +	 * The real_mode_data address is in %rsi and that register can be
> +	 * clobbered by the called function so be sure to save it.
> +	 */
> +	push	%rsi
> +	call	sme_get_me_mask
> +	pop	%rsi

Do we really need a call here? The mask is established at this point, so
it's either 0 when the encryption stuff is not compiled in or it can be
retrieved from a variable which is accessible at this point.

> +
> +	addq	$(init_top_pgt - __START_KERNEL_map), %rax
>  1:
>  
>  	/* Enable PAE mode, PGE and LA57 */

Thanks,

	tglx

[toc] | [next] | [standalone]

#1671787

On Wed, 21 Jun 2017, Tom Lendacky wrote:
> On 6/21/2017 2:16 AM, Thomas Gleixner wrote:
> > Why is this an unconditional function? Isn't the mask simply 0 when the MEM
> > ENCRYPT support is disabled?
> 
> I made it unconditional because of the call from head_64.S. I can't make
> use of the C level static inline function and since the mask is not a
> variable if CONFIG_AMD_MEM_ENCRYPT is not configured (#defined to 0) I
> can't reference the variable directly.
> 
> I could create a #define in head_64.S that changes this to load rax with
> the variable if CONFIG_AMD_MEM_ENCRYPT is configured or a zero if it's
> not or add a #ifdef at that point in the code directly. Thoughts on
> that?

See below.

> > That does not make any sense. Neither the call to sme_encrypt_kernel() nor
> > the following call to sme_get_me_mask().
> > 
> > __startup_64() is already C code, so why can't you simply call that from
> > __startup_64() in C and return the mask from there?
> 
> I was trying to keep it explicit as to what was happening, but I can
> move those calls into __startup_64().

That's much preferred. And the return value wants to be documented in both
C and ASM code.

> I'll still need the call to sme_get_me_mask() in the secondary_startup_64
> path, though (depending on your thoughts to the above response).

        call verify_cpu

        movq    $(init_top_pgt - __START_KERNEL_map), %rax

So if you make that:

	/*
	 * Sanitize CPU configuration and retrieve the modifier
	 * for the initial pgdir entry which will be programmed
	 * into CR3. Depends on enabled SME encryption, normally 0.
	 */
	call __startup_secondary_64

        addq    $(init_top_pgt - __START_KERNEL_map), %rax

You can hide that stuff in C-code nicely without adding any cruft to the
ASM code.

Thanks,

	tglx

[toc] | [prev] | [next] | [standalone]

#1671954

On Wed, 21 Jun 2017, Tom Lendacky wrote:
> On 6/21/2017 10:38 AM, Thomas Gleixner wrote:
> > 	/*
> > 	 * Sanitize CPU configuration and retrieve the modifier
> > 	 * for the initial pgdir entry which will be programmed
> > 	 * into CR3. Depends on enabled SME encryption, normally 0.
> > 	 */
> > 	call __startup_secondary_64
> > 
> >          addq    $(init_top_pgt - __START_KERNEL_map), %rax
> > 
> > You can hide that stuff in C-code nicely without adding any cruft to the
> > ASM code.
> > 
> 
> Moving the call to verify_cpu into the C-code might be quite a bit of
> change.  Currently, the verify_cpu code is included code and not a
> global function.

Ah. Ok. I missed that.

> I can still do the __startup_secondary_64() function and then look to
> incorporate verify_cpu into both __startup_64() and
> __startup_secondary_64() as a post-patch to this series.

Yes, just having __startup_secondary_64() for now and there the extra bits
for that encryption stuff is fine.

> At least the secondary path will have a base C routine to which
> modifications can be made in the future if needed.  How does that sound?

Sounds like a plan.

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web