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

[Marc Orr <marcorr@google.com>]

On Mon, Jun 20, 2022 at 4:02 PM Ashish Kalra <Ashish.Kalra@amd.com> wrote:
>
> From: Brijesh Singh <brijesh.singh@amd.com>
>
> 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@amd.com>
> ---
>  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@amd.com>
> + */
> +
> +#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
>