Detect if 5-level paging is actually enabled on the host. #12310
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The CPUID can indicate support for 5-level paging (57 virtual address bits), but the kernel might not have it enabled. This change adds a check using `mmap` to see if addresses above 2^48 are usable. If not, `VirtualAddressBits` is capped at 48, even if CPUID suggests 57. Fixes #12308 PiperOrigin-RevId: 832518109
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Detect if 5-level paging is actually enabled on the host.
The CPUID can indicate support for 5-level paging (57 virtual address bits),
but the kernel might not have it enabled. This change adds a check using
mmapto see if addresses above 2^48 are usable. If not,VirtualAddressBitsis capped at 48, even if CPUID suggests 57.Fixes #12308