Re: [PATCH Part2 v5 04/45] x86/sev: Add RMP entry lookup helpers

[Jarkko Sakkinen]

On Fri, Aug 20, 2021 at 10:58:37AM -0500, Brijesh Singh wrote:
> The snp_lookup_page_in_rmptable() can be used by the host to read the RMP
> entry for a given page. The RMP entry format is documented in AMD PPR, see
> https://bugzilla.kernel.org/attachment.cgi?id=296015.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> ---
>  arch/x86/include/asm/sev.h | 27 ++++++++++++++++++++++++
>  arch/x86/kernel/sev.c      | 43 ++++++++++++++++++++++++++++++++++++++
>  include/linux/sev.h        | 30 ++++++++++++++++++++++++++
>  3 files changed, 100 insertions(+)
>  create mode 100644 include/linux/sev.h
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index a5f0a1c3ccbe..5b1a6a075c47 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -9,6 +9,7 @@
>  #define __ASM_ENCRYPTED_STATE_H
>  
>  #include <linux/types.h>
> +#include <linux/sev.h>
>  #include <asm/insn.h>
>  #include <asm/sev-common.h>
>  #include <asm/bootparam.h>
> @@ -77,6 +78,32 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
>  
>  /* RMP page size */
>  #define RMP_PG_SIZE_4K			0
> +#define RMP_TO_X86_PG_LEVEL(level)	(((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)
> +
> +/*
> + * The RMP entry format is not architectural. The format is defined in PPR
> + * Family 19h Model 01h, Rev B1 processor.
> + */
> +struct __packed rmpentry {
> +	union {
> +		struct {
> +			u64	assigned	: 1,
> +				pagesize	: 1,
> +				immutable	: 1,
> +				rsvd1		: 9,
> +				gpa		: 39,
> +				asid		: 10,
> +				vmsa		: 1,
> +				validated	: 1,
> +				rsvd2		: 1;
> +		} info;
> +		u64 low;
> +	};
> +	u64 high;
> +};
> +
> +#define rmpentry_assigned(x)	((x)->info.assigned)
> +#define rmpentry_pagesize(x)	((x)->info.pagesize)
>  
>  #define RMPADJUST_VMSA_PAGE_BIT		BIT(16)
>  
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 7936c8139c74..f383d2a89263 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -54,6 +54,8 @@
>   * bookkeeping, the range need to be added during the RMP entry lookup.
>   */
>  #define RMPTABLE_CPU_BOOKKEEPING_SZ	0x4000
> +#define RMPENTRY_SHIFT			8
> +#define rmptable_page_offset(x)	(RMPTABLE_CPU_BOOKKEEPING_SZ + (((unsigned long)x) >> RMPENTRY_SHIFT))
>  
>  /* For early boot hypervisor communication in SEV-ES enabled guests */
>  static struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
> @@ -2376,3 +2378,44 @@ static int __init snp_rmptable_init(void)
>   * available after subsys_initcall().
>   */
>  fs_initcall(snp_rmptable_init);
> +
> +static struct rmpentry *__snp_lookup_rmpentry(u64 pfn, int *level)
> +{
> +	unsigned long vaddr, paddr = pfn << PAGE_SHIFT;
> +	struct rmpentry *entry, *large_entry;
> +
> +	if (!pfn_valid(pfn))
> +		return ERR_PTR(-EINVAL);
> +
> +	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> +		return ERR_PTR(-ENXIO);
> +
> +	vaddr = rmptable_start + rmptable_page_offset(paddr);
> +	if (unlikely(vaddr > rmptable_end))
> +		return ERR_PTR(-ENXIO);
> +
> +	entry = (struct rmpentry *)vaddr;
> +
> +	/* Read a large RMP entry to get the correct page level used in RMP entry. */
> +	vaddr = rmptable_start + rmptable_page_offset(paddr & PMD_MASK);
> +	large_entry = (struct rmpentry *)vaddr;
> +	*level = RMP_TO_X86_PG_LEVEL(rmpentry_pagesize(large_entry));
> +
> +	return entry;
> +}
> +
> +/*
> + * Return 1 if the RMP entry is assigned, 0 if it exists but is not assigned,
> + * and -errno if there is no corresponding RMP entry.

According to /usr/include/asm-generic/errno.h, there is 133
error codes. Why you need so many just to say that there
is no entry?

> + */
> +int snp_lookup_rmpentry(u64 pfn, int *level)
> +{
> +	struct rmpentry *e;
> +
> +	e = __snp_lookup_rmpentry(pfn, level);
> +	if (IS_ERR(e))
> +		return PTR_ERR(e);
> +
> +	return !!rmpentry_assigned(e);
> +}
> +EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);
> diff --git a/include/linux/sev.h b/include/linux/sev.h
> new file mode 100644
> index 000000000000..1a68842789e1
> --- /dev/null
> +++ b/include/linux/sev.h
> @@ -0,0 +1,30 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * AMD Secure Encrypted Virtualization
> + *
> + * Author: Brijesh Singh <brijesh.singh@xxxxxxx>

nit: this is redundant.

Each git commit has an author-field.

> + */
> +
> +#ifndef __LINUX_SEV_H
> +#define __LINUX_SEV_H
> +
> +/* RMUPDATE detected 4K page and 2MB page overlap. */
> +#define RMPUPDATE_FAIL_OVERLAP		7
> +
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +int snp_lookup_rmpentry(u64 pfn, int *level);
> +int psmash(u64 pfn);
> +int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid, bool immutable);
> +int rmp_make_shared(u64 pfn, enum pg_level level);
> +#else
> +static inline int snp_lookup_rmpentry(u64 pfn, int *level) { return 0; }
> +static inline int psmash(u64 pfn) { return -ENXIO; }
> +static inline int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid,
> +				   bool immutable)
> +{
> +	return -ENODEV;
> +}
> +static inline int rmp_make_shared(u64 pfn, enum pg_level level) { return -ENODEV; }
> +
> +#endif /* CONFIG_AMD_MEM_ENCRYPT */
> +#endif /* __LINUX_SEV_H */
> -- 
> 2.17.1
> 

BR, Jarkko