Re: [PATCH Part2 v5 05/45] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction

Borislav Petkov
2021-09-24T14:04:15Z

On Fri, Aug 20, 2021 at 10:58:38AM -0500, Brijesh Singh wrote:
> The RMPUPDATE instruction writes a new RMP entry in the RMP Table. The
> hypervisor will use the instruction to add pages to the RMP table. See
> APM3 for details on the instruction operations.
>
> The PSMASH instruction expands a 2MB RMP entry into a corresponding set of
> contiguous 4KB-Page RMP entries. The hypervisor will use this instruction
> to adjust the RMP entry without invalidating the previous RMP entry.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/include/asm/sev.h | 11 ++++++
> arch/x86/kernel/sev.c | 72 ++++++++++++++++++++++++++++++++++++++
> 2 files changed, 83 insertions(+)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 5b1a6a075c47..92ced9626e95 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -78,7 +78,9 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
>
> /* RMP page size */
> #define RMP_PG_SIZE_4K 0
> +#define RMP_PG_SIZE_2M 1
> #define RMP_TO_X86_PG_LEVEL(level) (((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)
> +#define X86_TO_RMP_PG_LEVEL(level) (((level) == PG_LEVEL_4K) ? RMP_PG_SIZE_4K : RMP_PG_SIZE_2M)
>
> /*
> * The RMP entry format is not architectural. The format is defined in PPR
> @@ -107,6 +109,15 @@ struct __packed rmpentry {
>
> #define RMPADJUST_VMSA_PAGE_BIT BIT(16)
>
> +struct rmpupdate {

Function is called the same way - maybe this should be called
rmpupdate_desc or so.

> + u64 gpa;
> + u8 assigned;
> + u8 pagesize;
> + u8 immutable;
> + u8 rsvd;
> + u32 asid;
> +} __packed;
> +
> #ifdef CONFIG_AMD_MEM_ENCRYPT
> extern struct static_key_false sev_es_enable_key;
> extern void __sev_es_ist_enter(struct pt_regs *regs);
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index f383d2a89263..8627c49666c9 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -2419,3 +2419,75 @@ int snp_lookup_rmpentry(u64 pfn, int *level)
> return !!rmpentry_assigned(e);
> }
> EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);
> +

<--- kernel-doc comment.

> +int psmash(u64 pfn)
> +{
> + unsigned long paddr = pfn << PAGE_SHIFT;
> + int ret;
> +
> + if (!pfn_valid(pfn))
> + return -EINVAL;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> + return -ENXIO;

Make that the first check pls.

> +
> + /* Binutils version 2.36 supports the PSMASH mnemonic. */
> + asm volatile(".byte 0xF3, 0x0F, 0x01, 0xFF"
> + : "=a"(ret)
> + : "a"(paddr)
> + : "memory", "cc");
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(psmash);

That's for kvm?

> +static int rmpupdate(u64 pfn, struct rmpupdate *val)
> +{
> + unsigned long paddr = pfn << PAGE_SHIFT;
> + int ret;
> +
> + if (!pfn_valid(pfn))
> + return -EINVAL;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> + return -ENXIO;

Also first check.

> +
> + /* 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");
> + return ret;
> +}
> +
> +int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid, bool immutable)
> +{
> + struct rmpupdate val;
> +
> + if (!pfn_valid(pfn))
> + return -EINVAL;

rmpupdate() does that check too so choose one place please and kill the
other.

> + memset(&val, 0, sizeof(val));
> + val.assigned = 1;
> + val.asid = asid;
> + val.immutable = immutable;
> + val.gpa = gpa;
> + val.pagesize = X86_TO_RMP_PG_LEVEL(level);
> +
> + return rmpupdate(pfn, &val);
> +}
> +EXPORT_SYMBOL_GPL(rmp_make_private);
> +
> +int rmp_make_shared(u64 pfn, enum pg_level level)
> +{
> + struct rmpupdate val;
> +
> + if (!pfn_valid(pfn))
> + return -EINVAL;
> +
> + memset(&val, 0, sizeof(val));
> + val.pagesize = X86_TO_RMP_PG_LEVEL(level);
> +
> + return rmpupdate(pfn, &val);
> +}
> +EXPORT_SYMBOL_GPL(rmp_make_shared);

Both exports for kvm I assume?

Thx.

--
Regards/Gruss,
Boris.