Subj : Re: CPU Hog
To   : Digital Man
From : Tony Langdon
Date : Wed Aug 10 2022 19:06:00

-=> On 08-09-22 12:10, Digital Man wrote to Tony Langdon <=-

 DM> Unfortunately, no. 64-bit x86 processors, when operating in "long mode"
 DM> (64-bit mode) do not support the "virtual 86" mode that they have in
 DM> 32-bit mode. --

While not "virtual 8086 mode" as we've known it, from
https://en.wikipedia.org/wiki/Virtual_8086_mode#64-bit_and_VMX_support

"Virtual 8086 mode is not available in x86-64 long mode, although it is still
present on x86-64 capable processors running in legacy mode.

Intel VT-x brings back the ability to run virtual 8086 mode from x86-64 long
mode, but it has to be done by transitioning the (physical) processor to VMX
root mode and launching a logical (virtual) processor itself running in virtual
8086 mode.[14]

Westmere and later Intel processors usually[15] can start the virtual processor
directly in real mode using the "unrestricted guest" feature (which itself
requires Extended Page Tables); this method removes the need to resort to the
nested virtual 8086 mode simply to run the legacy BIOS for booting.[16][17]

AMD-V can do virtual 8086 mode in guests, too, but it can also just run the
guest in "paged real mode" using the following steps: you create a SVM (Secure
Virtual Machine) mode guest with CR0.PE=0, but CR0.PG=1 (that is, with
protected mode disabled but paging enabled), which is ordinarily impossible,
but is allowed for SVM guests if the host intercepts page faults.[18] "



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