Re: [PATCH Part2 v6 05/49] x86/sev: Add RMP entry lookup helpers

From: Marc Orr
Date: Thu Jun 23 2022 - 17:30:36 EST

On Mon, Jun 20, 2022 at 4:02 PM Ashish Kalra <Ashish.Kalra@xxxxxxx> wrote:
>
> From: Brijesh Singh <brijesh.singh@xxxxxxx>
>
> 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 9c2d33f1cfee..cb16f0e5b585 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>
> @@ -84,6 +85,32 @@ 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 25c7feb367f6..59e7ec6b0326 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -65,6 +65,8 @@
> * 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);
> @@ -2386,3 +2388,44 @@ 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);

nit: I think we should check if SNP is enabled first, before doing
anything else. In other words, I think we should move this check above
the `!pfn_valid()` check.

> +
> + vaddr = rmptable_start + rmptable_page_offset(paddr);
> + if (unlikely(vaddr > rmptable_end))
> + return ERR_PTR(-ENXIO);

nit: It would be nice to use a different error code here, from the SNP
feature check. That way, if this function fails, it's easier to
diagnose where the function failed from the error code.

> +
> + 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.
> + */
> +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>
> + */
> +
> +#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);

nit: I think the declarations for `psmash()`, `rmp_make_private()`,
and `rmp_make_shared()` should be introduced in the patches that have
their definitions.

> +#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 */
> --
> 2.25.1
>