linux-kernel - Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map when adding it to RMP table

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Date:   Wed, 27 Jul 2022 19:01:34 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
        rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com,
        michael.roth@....com, vbabka@...e.cz, kirill@...temov.name,
        ak@...ux.intel.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, jarkko@...nel.org
Subject: Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map
 when adding it to RMP table

On Mon, Jun 20, 2022 at 11:03:07PM +0000, Ashish Kalra wrote:

> Subject: x86/sev: Invalid pages from direct map when adding it to RMP table

"...: Invalidate pages from the direct map when adding them to the RMP table"

> +static int restore_direct_map(u64 pfn, int npages)
> +{
> +	int i, ret = 0;
> +
> +	for (i = 0; i < npages; i++) {
> +		ret = set_direct_map_default_noflush(pfn_to_page(pfn + i));

set_memory_p() ?

> +		if (ret)
> +			goto cleanup;
> +	}
> +
> +cleanup:
> +	WARN(ret > 0, "Failed to restore direct map for pfn 0x%llx\n", pfn + i);

Warn for each pfn?!

That'll flood dmesg mightily.

> +	return ret;
> +}
> +
> +static int invalid_direct_map(unsigned long pfn, int npages)
> +{
> +	int i, ret = 0;
> +
> +	for (i = 0; i < npages; i++) {
> +		ret = set_direct_map_invalid_noflush(pfn_to_page(pfn + i));

As above, set_memory_np() doesn't work here instead of looping over each
page?

> @@ -2462,11 +2494,38 @@ static int rmpupdate(u64 pfn, struct rmpupdate *val)
>  	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
>  		return -ENXIO;
>  
> +	level = RMP_TO_X86_PG_LEVEL(val->pagesize);
> +	npages = page_level_size(level) / PAGE_SIZE;
> +
> +	/*
> +	 * If page is getting assigned in the RMP table then unmap it from the
> +	 * direct map.
> +	 */
> +	if (val->assigned) {
> +		if (invalid_direct_map(pfn, npages)) {
> +			pr_err("Failed to unmap pfn 0x%llx pages %d from direct_map\n",

"Failed to unmap %d pages at pfn 0x... from the direct map\n"

> +			       pfn, npages);
> +			return -EFAULT;
> +		}
> +	}
> +
>  	/* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
>  	asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
>  		     : "=a"(ret)
>  		     : "a"(paddr), "c"((unsigned long)val)
>  		     : "memory", "cc");
> +
> +	/*
> +	 * Restore the direct map after the page is removed from the RMP table.
> +	 */
> +	if (!ret && !val->assigned) {
> +		if (restore_direct_map(pfn, npages)) {
> +			pr_err("Failed to map pfn 0x%llx pages %d in direct_map\n",

"Failed to map %d pages at pfn 0x... into the direct map\n"

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette