Re: [PATCH v10 07/50] x86/sev: Add RMP entry lookup helpers

[Borislav Petkov]

On Mon, Oct 16, 2023 at 08:27:36AM -0500, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@xxxxxxx>
> 
> The snp_lookup_page_in_rmptable() can be used by the host to read the RMP

$ git grep snp_lookup_page_in_rmptable
$

Stale commit message. And not very telling. Please rewrite.

> entry for a given page. The RMP entry format is documented in AMD PPR, see
> https://bugzilla.kernel.org/attachment.cgi?id=296015.

<--- Brijesh's SOB comes first here if he's the primary author.

> Co-developed-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> [mdr: separate 'assigned' indicator from return code]
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
>  arch/x86/include/asm/sev-common.h |  4 +++
>  arch/x86/include/asm/sev-host.h   | 22 +++++++++++++
>  arch/x86/virt/svm/sev.c           | 53 +++++++++++++++++++++++++++++++
>  3 files changed, 79 insertions(+)
>  create mode 100644 arch/x86/include/asm/sev-host.h
> 
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index b463fcbd4b90..1e6fb93d8ab0 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -173,4 +173,8 @@ struct snp_psc_desc {
>  #define GHCB_ERR_INVALID_INPUT		5
>  #define GHCB_ERR_INVALID_EVENT		6
>  
> +/* RMP page size */
> +#define RMP_PG_SIZE_4K			0

RMP_PG_LEVEL_4K just like the generic ones.

> +#define RMP_TO_X86_PG_LEVEL(level)	(((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)

What else is there besides X86 PG level?

IOW, RMP_TO_PG_LEVEL simply.

> +
>  #endif
> diff --git a/arch/x86/include/asm/sev-host.h b/arch/x86/include/asm/sev-host.h

Nah, we don't need a third sev header:

arch/x86/include/asm/sev-common.h
arch/x86/include/asm/sev.h
arch/x86/include/asm/sev-host.h

Put it in sev.h pls.

sev-common.h should be merged into sev.h too unless there's a compelling
reason not to which I don't see atm.

> new file mode 100644
> index 000000000000..4c487ce8457f
> --- /dev/null
> +++ b/arch/x86/include/asm/sev-host.h

...

> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> index 8b9ed72489e4..7d3802605376 100644
> --- a/arch/x86/virt/svm/sev.c
> +++ b/arch/x86/virt/svm/sev.c
> @@ -53,6 +53,9 @@ struct rmpentry {
>   */
>  #define RMPTABLE_CPU_BOOKKEEPING_SZ	0x4000
>  
> +/* Mask to apply to a PFN to get the first PFN of a 2MB page */
> +#define PFN_PMD_MASK	(~((1ULL << (PMD_SHIFT - PAGE_SHIFT)) - 1))

GENMASK_ULL

>  static struct rmpentry *rmptable_start __ro_after_init;
>  static u64 rmptable_max_pfn __ro_after_init;
>  
> @@ -237,3 +240,53 @@ static int __init snp_rmptable_init(void)
>   * the page(s) used for DMA are hypervisor owned.
>   */
>  fs_initcall(snp_rmptable_init);
> +
> +static int rmptable_entry(u64 pfn, struct rmpentry *entry)

The signature of this one should be:

static struct rmpentry *get_rmp_entry(u64 pfn)

and the callers should use the IS_ERR* macros to check whether it
returns a valid pointer or a negative value for error.

Ditto for the other two functions here.

> +	if (WARN_ON_ONCE(pfn > rmptable_max_pfn))
> +		return -EFAULT;
> +
> +	*entry = rmptable_start[pfn];

This wants to be called rmptable[] then.

> +
> +	return 0;
> +}
> +
> +static int __snp_lookup_rmpentry(u64 pfn, struct rmpentry *entry, int *level)
> +{
> +	struct rmpentry large_entry;
> +	int ret;
> +
> +	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> +		return -ENXIO;

ENODEV or so.

> +
> +	ret = rmptable_entry(pfn, entry);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Find the authoritative RMP entry for a PFN. This can be either a 4K
> +	 * RMP entry or a special large RMP entry that is authoritative for a
> +	 * whole 2M area.
> +	 */
> +	ret = rmptable_entry(pfn & PFN_PMD_MASK, &large_entry);
> +	if (ret)
> +		return ret;
> +
> +	*level = RMP_TO_X86_PG_LEVEL(large_entry.pagesize);
> +
> +	return 0;
> +}
> +
> +int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level)
> +{
> +	struct rmpentry e;
> +	int ret;
> +
> +	ret = __snp_lookup_rmpentry(pfn, &e, level);
> +	if (ret)
> +		return ret;
> +
> +	*assigned = !!e.assigned;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);
> -- 

Thx.

-- 
Regards/Gruss,
    Boris.

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