linux-kernel - Re: [PATCH Part1 RFC v2 11/20] x86/compressed: Add helper for validating pages in the decompression stage

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Message-ID: <YKah5QInPK4+7xaC@zn.tnic>
Date:   Thu, 20 May 2021 19:52:37 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, jroedel@...e.de, thomas.lendacky@....com,
        pbonzini@...hat.com, mingo@...hat.com, dave.hansen@...el.com,
        rientjes@...gle.com, seanjc@...gle.com, peterz@...radead.org,
        hpa@...or.com, tony.luck@...el.com
Subject: Re: [PATCH Part1 RFC v2 11/20] x86/compressed: Add helper for
 validating pages in the decompression stage

On Fri, Apr 30, 2021 at 07:16:07AM -0500, Brijesh Singh wrote:
> @@ -278,12 +279,28 @@ static int set_clr_page_flags(struct x86_mapping_info *info,
>  	if ((set | clr) & _PAGE_ENC)
>  		clflush_page(address);
>  
> +	/*
> +	 * If the encryption attribute is being cleared, then change the page state to
> +	 * shared in the RMP entry. Change of the page state must be done before the
> +	 * PTE updates.
> +	 */
> +	if (clr & _PAGE_ENC)
> +		snp_set_page_shared(pte_pfn(*ptep) << PAGE_SHIFT);

>From the last review:

The statement above already looks at clr - just merge the two together.

> @@ -136,6 +137,55 @@ static inline bool sev_snp_enabled(void)
>  	return sev_status_val & MSR_AMD64_SEV_SNP_ENABLED ? true : false;
>  }
>  
> +static void snp_page_state_change(unsigned long paddr, int op)

>From the last review:

no need for too many prefixes on static functions - just call this one
__change_page_state() or so, so that the below one can be called...

> +{
> +	u64 val;
> +
> +	if (!sev_snp_enabled())
> +		return;
> +
> +	/*
> +	 * If the page is getting changed from private to shard then invalidate the page

							shared

And you can write this a lot shorter

	* If private -> shared, ...

> +	 * before requesting the state change in the RMP table.
> +	 */
> +	if ((op == SNP_PAGE_STATE_SHARED) && pvalidate(paddr, RMP_PG_SIZE_4K, 0))
> +		goto e_pvalidate;
> +
> +	/* Issue VMGEXIT to change the page state in RMP table. */
> +	sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
> +	VMGEXIT();
> +
> +	/* Read the response of the VMGEXIT. */
> +	val = sev_es_rd_ghcb_msr();
> +	if ((GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP) || GHCB_MSR_PSC_RESP_VAL(val))
> +		goto e_psc;

That label is used only once - just do the termination here directly and
remove it.

Thx.

-- 
Regards/Gruss,
    Boris.

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