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SubjectRe: [PATCH v7 71/72] x86/efi: Add GHCB mappings when SEV-ES is active
+ Ard so that he can ack the efi bits.

On Mon, Sep 07, 2020 at 03:16:12PM +0200, Joerg Roedel wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
>
> Calling down to EFI runtime services can result in the firmware performing
> VMGEXIT calls. The firmware is likely to use the GHCB of the OS (e.g., for
> setting EFI variables), so each GHCB in the system needs to be identity
> mapped in the EFI page tables, as unencrypted, to avoid page faults.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> [ jroedel@suse.de: Moved GHCB mapping loop to sev-es.c ]
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> arch/x86/boot/compressed/sev-es.c | 1 +
> arch/x86/include/asm/sev-es.h | 2 ++
> arch/x86/kernel/sev-es.c | 30 ++++++++++++++++++++++++++++++
> arch/x86/platform/efi/efi_64.c | 10 ++++++++++
> 4 files changed, 43 insertions(+)
>
> diff --git a/arch/x86/boot/compressed/sev-es.c b/arch/x86/boot/compressed/sev-es.c
> index 45702b866c33..0a9a248ca33d 100644
> --- a/arch/x86/boot/compressed/sev-es.c
> +++ b/arch/x86/boot/compressed/sev-es.c
> @@ -12,6 +12,7 @@
> */
> #include "misc.h"
>
> +#include <asm/pgtable_types.h>
> #include <asm/sev-es.h>
> #include <asm/trapnr.h>
> #include <asm/trap_pf.h>
> diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
> index e919f09ae33c..cf1d957c7091 100644
> --- a/arch/x86/include/asm/sev-es.h
> +++ b/arch/x86/include/asm/sev-es.h
> @@ -102,11 +102,13 @@ static __always_inline void sev_es_nmi_complete(void)
> if (static_branch_unlikely(&sev_es_enable_key))
> __sev_es_nmi_complete();
> }
> +extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
> #else
> static inline void sev_es_ist_enter(struct pt_regs *regs) { }
> static inline void sev_es_ist_exit(void) { }
> static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { return 0; }
> static inline void sev_es_nmi_complete(void) { }
> +static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
> #endif
>
> #endif
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index 9ab3a4dfecd8..4e2b7e4d9b87 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -491,6 +491,36 @@ int sev_es_setup_ap_jump_table(struct real_mode_header *rmh)
> return 0;
> }
>
> +/*
> + * This is needed by the OVMF UEFI firmware which will use whatever it finds in
> + * the GHCB MSR as its GHCB to talk to the hypervisor. So make sure the per-cpu
> + * runtime GHCBs used by the kernel are also mapped in the EFI page-table.
> + */
> +int __init sev_es_efi_map_ghcbs(pgd_t *pgd)
> +{
> + struct sev_es_runtime_data *data;
> + unsigned long address, pflags;
> + int cpu;
> + u64 pfn;
> +
> + if (!sev_es_active())
> + return 0;
> +
> + pflags = _PAGE_NX | _PAGE_RW;
> +
> + for_each_possible_cpu(cpu) {
> + data = per_cpu(runtime_data, cpu);
> +
> + address = __pa(&data->ghcb_page);
> + pfn = address >> PAGE_SHIFT;
> +
> + if (kernel_map_pages_in_pgd(pgd, pfn, address, 1, pflags))
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
> {
> struct pt_regs *regs = ctxt->regs;
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 6af4da1149ba..8f5759df7776 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -47,6 +47,7 @@
> #include <asm/realmode.h>
> #include <asm/time.h>
> #include <asm/pgalloc.h>
> +#include <asm/sev-es.h>
>
> /*
> * We allocate runtime services regions top-down, starting from -4G, i.e.
> @@ -229,6 +230,15 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
> return 1;
> }
>
> + /*
> + * When SEV-ES is active, the GHCB as set by the kernel will be used
> + * by firmware. Create a 1:1 unencrypted mapping for each GHCB.
> + */
> + if (sev_es_efi_map_ghcbs(pgd)) {
> + pr_err("Failed to create 1:1 mapping for the GHCBs!\n");
> + return 1;
> + }
> +
> /*
> * When making calls to the firmware everything needs to be 1:1
> * mapped and addressable with 32-bit pointers. Map the kernel
> --
> 2.28.0
>

--
Regards/Gruss,
Boris.

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

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