Re: [PATCH RFC 32/55] efi: switch EFI L4 table to use new APIs

["Nuernberger, Stefan" <snu@amazon.de>]

On Thu, 2019-02-07 at 16:44 +0000, Wei Liu wrote:
> This requires storing the MFN instead of linear address of the L4
> table. Adjust code accordingly.
> 
> Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> ---
>  xen/arch/x86/efi/runtime.h | 12 +++++++++---
>  xen/common/efi/boot.c      |  8 ++++++--
>  xen/common/efi/efi.h       |  3 ++-
>  xen/common/efi/runtime.c   |  8 ++++----
>  4 files changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/xen/arch/x86/efi/runtime.h b/xen/arch/x86/efi/runtime.h
> index d9eb8f5c27..277d237953 100644
> --- a/xen/arch/x86/efi/runtime.h
> +++ b/xen/arch/x86/efi/runtime.h
> @@ -2,11 +2,17 @@
>  #include <asm/mc146818rtc.h>
>  
>  #ifndef COMPAT
> -l4_pgentry_t *__read_mostly efi_l4_pgtable;
> +mfn_t __read_mostly efi_l4_mfn = INVALID_MFN_INITIALIZER;
>  
>  void efi_update_l4_pgtable(unsigned int l4idx, l4_pgentry_t l4e)
>  {
> -    if ( efi_l4_pgtable )
> -        l4e_write(efi_l4_pgtable + l4idx, l4e);
> +    if ( !mfn_eq(efi_l4_mfn, INVALID_MFN) )
> +    {
> +        l4_pgentry_t *l4t;
> +
> +        l4t = map_xen_pagetable_new(efi_l4_mfn);
> +        l4e_write(l4t + l4idx, l4e);
> +        UNMAP_XEN_PAGETABLE_NEW(l4t);

nit: This doesn't need the implicit NULL assignment. The non-macro
unmap_xen_pagetable_new is sufficient here. Do you have a guideline on
when to use the macro over the function call? I assume the compiler
eliminates most of the dead stores on function return.

- Stefan

> +    }
>  }
>  #endif
> diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
> index 3868293d06..f55d6a6d76 100644
> --- a/xen/common/efi/boot.c
> +++ b/xen/common/efi/boot.c
> @@ -1488,6 +1488,7 @@ void __init efi_init_memory(void)
>          unsigned int prot;
>      } *extra, *extra_head = NULL;
>  #endif
> +    l4_pgentry_t *efi_l4_pgtable;
>  
>      free_ebmalloc_unused_mem();
>  
> @@ -1603,8 +1604,9 @@ void __init efi_init_memory(void)
>                                   mdesc_ver, efi_memmap);
>  #else
>      /* Set up 1:1 page tables to do runtime calls in "physical"
> mode. */
> -    efi_l4_pgtable = alloc_xen_pagetable();
> -    BUG_ON(!efi_l4_pgtable);
> +    efi_l4_mfn = alloc_xen_pagetable_new();
> +    BUG_ON(mfn_eq(efi_l4_mfn, INVALID_MFN));
> +    efi_l4_pgtable = map_xen_pagetable_new(efi_l4_mfn);
>      clear_page(efi_l4_pgtable);
>  
>      copy_mapping(efi_l4_pgtable, 0, max_page, ram_range_valid);
> @@ -1703,6 +1705,8 @@ void __init efi_init_memory(void)
>            i < l4_table_offset(DIRECTMAP_VIRT_END); ++i )
>          efi_l4_pgtable[i] = idle_pg_table[i];
>  #endif
> +
> +    UNMAP_XEN_PAGETABLE_NEW(efi_l4_pgtable);
>  }
>  #endif
>  
> diff --git a/xen/common/efi/efi.h b/xen/common/efi/efi.h
> index 6b9c56ead1..139b660ed7 100644
> --- a/xen/common/efi/efi.h
> +++ b/xen/common/efi/efi.h
> @@ -6,6 +6,7 @@
>  #include <efi/eficapsule.h>
>  #include <efi/efiapi.h>
>  #include <xen/efi.h>
> +#include <xen/mm.h>
>  #include <xen/spinlock.h>
>  #include <asm/page.h>
>  
> @@ -29,7 +30,7 @@ extern UINTN efi_memmap_size, efi_mdesc_size;
>  extern void *efi_memmap;
>  
>  #ifdef CONFIG_X86
> -extern l4_pgentry_t *efi_l4_pgtable;
> +extern mfn_t efi_l4_mfn;
>  #endif
>  
>  extern const struct efi_pci_rom *efi_pci_roms;
> diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
> index 3d118d571d..8263f1d863 100644
> --- a/xen/common/efi/runtime.c
> +++ b/xen/common/efi/runtime.c
> @@ -85,7 +85,7 @@ struct efi_rs_state efi_rs_enter(void)
>      static const u32 mxcsr = MXCSR_DEFAULT;
>      struct efi_rs_state state = { .cr3 = 0 };
>  
> -    if ( !efi_l4_pgtable )
> +    if ( mfn_eq(efi_l4_mfn, INVALID_MFN) )
>          return state;
>  
>      state.cr3 = read_cr3();
> @@ -111,7 +111,7 @@ struct efi_rs_state efi_rs_enter(void)
>          lgdt(&gdt_desc);
>      }
>  
> -    switch_cr3_cr4(virt_to_maddr(efi_l4_pgtable), read_cr4());
> +    switch_cr3_cr4(mfn_to_maddr(efi_l4_mfn), read_cr4());
>  
>      return state;
>  }
> @@ -140,9 +140,9 @@ void efi_rs_leave(struct efi_rs_state *state)
>  
>  bool efi_rs_using_pgtables(void)
>  {
> -    return efi_l4_pgtable &&
> +    return !mfn_eq(efi_l4_mfn, INVALID_MFN) &&
>             (smp_processor_id() == efi_rs_on_cpu) &&
> -           (read_cr3() == virt_to_maddr(efi_l4_pgtable));
> +           (read_cr3() == mfn_to_maddr(efi_l4_mfn));
>  }
>  
>  unsigned long efi_get_time(void)



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