[Xen-devel] Question about linear mapping of shadow page tables for 64bit HVM guest

[Abe Petrov <abe.petrov@xxxxxxxxx>]

Linear mapping of shadow page tables is used to find shadow PTEs that
map a given guest VA. If I understand the following macros correctly

    #define __sh_linear_l1_table ((shadow_l1e_t *)(SH_LINEAR_PT_VIRT_START))
    #define __sh_linear_l2_table ((shadow_l2e_t *)
          \
        (__sh_linear_l1_table +
shadow_l1_linear_offset(SH_LINEAR_PT_VIRT_START)))

there is an overlap between L1 and L2 (also L3 and L4) tables. That
creates potential conflicts between different guest VAs.

For example L1 shadow PTE for guest VA1 = 0x818000000000 (the same as
SH_LINEAR_PT_VIRT_START) coincides with L2 shadow PTE for the guest
VA2 = 0x0. So updating L1 shadow PTE for guest VA1 would overwrite L2
shadow PTE for the guest VA2.

What am I missing? Sorry for the novice question.

Thank you,

Abe.

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