linux-kernel - Re: [PATCHv3 02/32] x86/coco: Add API to handle encryption mask

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Date:   Fri, 18 Feb 2022 12:36:02 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        luto@...nel.org, peterz@...radead.org
Cc:     sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 02/32] x86/coco: Add API to handle encryption mask

On 2/18/22 08:16, Kirill A. Shutemov wrote:
> +#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
> +u64 cc_get_mask(bool enc);
> +u64 cc_mkenc(u64 val);
> +u64 cc_mkdec(u64 val);
> +#else
> +#define cc_get_mask(enc)	0
> +#define cc_mkenc(val)		(val)
> +#define cc_mkdec(val)		(val)
> +#endif

Is there a reason the stubs as #defines?  Static inlines are preferred
for consistent type safety among other things.

It would also be nice to talk about the u64 type in the changelog.  If I
remember right, there was a reason you didn't want to have a pgprot_t
here.

...
> @@ -74,12 +72,52 @@ static bool hyperv_cc_platform_has(enum cc_attr attr)
>  
>  bool cc_platform_has(enum cc_attr attr)
>  {
> -	if (sme_me_mask)
> +	switch (cc_vendor) {
> +	case CC_VENDOR_AMD:
>  		return amd_cc_platform_has(attr);
> -
> -	if (hv_is_isolation_supported())
> +	case CC_VENDOR_INTEL:
> +		return intel_cc_platform_has(attr);
> +	case CC_VENDOR_HYPERV:
>  		return hyperv_cc_platform_has(attr);
> -
> -	return false;
> +	default:
> +		return false;
> +	}
>  }
>  EXPORT_SYMBOL_GPL(cc_platform_has);

This patch is bordering on doing too many different things.  Adding the
CC_VENDOR_*'s in a separate patch probably would have been nice, for
instance.

This wasn't really broached at all in the changelog.

> +u64 cc_get_mask(bool enc)
> +{
> +	switch (cc_vendor) {
> +	case CC_VENDOR_AMD:
> +		return enc ? cc_mask : 0;
> +	default:
> +		return 0;
> +	}
> +}

I had to ask myself why you need all three of these functions.  It's
obvious _after_ reading the whole patch, but it left me wanting more in
the changelog about it.

> +u64 cc_mkenc(u64 val)
> +{
> +	switch (cc_vendor) {
> +	case CC_VENDOR_AMD:
> +		return val | cc_mask;
> +	default:
> +		return val;
> +	}
> +}
> +
> +u64 cc_mkdec(u64 val)
> +{
> +	switch (cc_vendor) {
> +	case CC_VENDOR_AMD:
> +		return val & ~cc_mask;
> +	default:
> +		return val;
> +	}
> +}
> +EXPORT_SYMBOL_GPL(cc_mkdec);
> +
> +__init void cc_init(enum cc_vendor vendor, u64 mask)
> +{
> +	cc_vendor = vendor;
> +	cc_mask = mask;
> +}
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 5a99f993e639..9af6be143998 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -33,6 +33,7 @@
>  #include <asm/nmi.h>
>  #include <clocksource/hyperv_timer.h>
>  #include <asm/numa.h>
> +#include <asm/coco.h>
>  
>  /* Is Linux running as the root partition? */
>  bool hv_root_partition;
> @@ -344,6 +345,8 @@ static void __init ms_hyperv_init_platform(void)
>  		 */
>  		swiotlb_force = SWIOTLB_FORCE;
>  #endif
> +		if (hv_get_isolation_type() != HV_ISOLATION_TYPE_NONE)
> +			cc_init(CC_VENDOR_HYPERV, 0);
>  	}
>  
>  	if (hv_max_functions_eax >= HYPERV_CPUID_NESTED_FEATURES) {
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index 3f0abb403340..fa758247ab57 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -44,6 +44,7 @@
>  #include <asm/setup.h>
>  #include <asm/sections.h>
>  #include <asm/cmdline.h>
> +#include <asm/coco.h>
>  
>  #include "mm_internal.h"
>  
> @@ -565,8 +566,7 @@ void __init sme_enable(struct boot_params *bp)
>  	} else {
>  		/* SEV state cannot be controlled by a command line option */
>  		sme_me_mask = me_mask;
> -		physical_mask &= ~sme_me_mask;
> -		return;
> +		goto out;
>  	}
>  
>  	/*
> @@ -600,6 +600,8 @@ void __init sme_enable(struct boot_params *bp)
>  		sme_me_mask = 0;
>  	else
>  		sme_me_mask = active_by_default ? me_mask : 0;
> -
> +out:
>  	physical_mask &= ~sme_me_mask;
> +	if (sme_me_mask)
> +		cc_init(CC_VENDOR_AMD, sme_me_mask);
>  }

I don't think you need to mop it up here, but where does this leave
sme_me_mask?

> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index b4072115c8ef..e79366b8a9da 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -1999,8 +1999,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>  	memset(&cpa, 0, sizeof(cpa));
>  	cpa.vaddr = &addr;
>  	cpa.numpages = numpages;
> -	cpa.mask_set = enc ? __pgprot(_PAGE_ENC) : __pgprot(0);
> -	cpa.mask_clr = enc ? __pgprot(0) : __pgprot(_PAGE_ENC);
> +	cpa.mask_set = __pgprot(cc_get_mask(enc));
> +	cpa.mask_clr = __pgprot(cc_get_mask(!enc));
>  	cpa.pgd = init_mm.pgd;
>  
>  	/* Must avoid aliasing mappings in the highmem code */

This actually ended up looking pretty nice.  It was a real mess along
the way, but this makes me think this is a _good_ solution.