Re: [PATCH Part1 RFC v4 09/36] x86/compressed: Add helper for validating pages in the decompression stage

[Borislav Petkov]

On Wed, Jul 07, 2021 at 01:14:39PM -0500, Brijesh Singh wrote:
> @@ -274,16 +274,31 @@ static int set_clr_page_flags(struct x86_mapping_info *info,
>  	/*
>  	 * Changing encryption attributes of a page requires to flush it from
>  	 * the caches.
> +	 *
> +	 * If the encryption attribute is being cleared, then change the page
> +	 * state to shared in the RMP table.

That comment...

>  	 */
> -	if ((set | clr) & _PAGE_ENC)
> +	if ((set | clr) & _PAGE_ENC) {
>  		clflush_page(address);
>  

... goes here:

<---

> +		if (clr)
> +			snp_set_page_shared(pte_pfn(*ptep) << PAGE_SHIFT);
> +	}
> +

...

> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index 2f3081e9c78c..f386d45a57b6 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -164,6 +164,47 @@ static bool is_vmpl0(void)
>  	return true;
>  }
>  
> +static void __page_state_change(unsigned long paddr, int op)

That op should be:

enum psc_op {
	SNP_PAGE_STATE_SHARED,
	SNP_PAGE_STATE_PRIVATE,
};

and have

static void __page_state_change(unsigned long paddr, enum psc_op op)

so that the compiler can check you're at least passing from the correct
set of defines.

> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index ea508835ab33..aee07d1bb138 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -45,6 +45,23 @@
>  		(((unsigned long)reg & GHCB_MSR_CPUID_REG_MASK) << GHCB_MSR_CPUID_REG_POS) | \
>  		(((unsigned long)fn) << GHCB_MSR_CPUID_FUNC_POS))
>  
> +/* SNP Page State Change */
> +#define GHCB_MSR_PSC_REQ		0x014
> +#define SNP_PAGE_STATE_PRIVATE		1
> +#define SNP_PAGE_STATE_SHARED		2
> +#define GHCB_MSR_PSC_GFN_POS		12
> +#define GHCB_MSR_PSC_GFN_MASK		GENMASK_ULL(39, 0)
> +#define GHCB_MSR_PSC_OP_POS		52
> +#define GHCB_MSR_PSC_OP_MASK		0xf
> +#define GHCB_MSR_PSC_REQ_GFN(gfn, op)	\
> +	(((unsigned long)((op) & GHCB_MSR_PSC_OP_MASK) << GHCB_MSR_PSC_OP_POS) | \
> +	((unsigned long)((gfn) & GHCB_MSR_PSC_GFN_MASK) << GHCB_MSR_PSC_GFN_POS) | \
> +	GHCB_MSR_PSC_REQ)
> +
> +#define GHCB_MSR_PSC_RESP		0x015
> +#define GHCB_MSR_PSC_ERROR_POS		32
> +#define GHCB_MSR_PSC_RESP_VAL(val)	((val) >> GHCB_MSR_PSC_ERROR_POS)
> +

Also get rid of eccessive defines...

-- 
Regards/Gruss,
    Boris.

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