robin.thoni/ipxe - git rthoni.com

Michael Brown 5a08b63cb7 [librm] Speed up protected-to-real mode transition under KVM On an Intel CPU supporting VMX, KVM will emulate instructions while the CPU state remains "invalid". In real mode, the CPU state is defined to be "invalid" if any segment register has a base which is not equal to (sreg<<4) or a limit which is not equal to 64kB. We don't actually use the base stored in the REAL_DS descriptor for any significant purpose. Change the base stored in this descriptor to be equal to (REAL_DS<<4). A segment register loaded with REAL_DS is then automatically valid in both real and protected modes. This allows KVM to stop emulating instructions much sooner. The only use of REAL_DS for memory accesses currently occurs in the indirect ljmp within prot_to_real. Change this to a direct ljmp, storing rm_cs in .text16 as part of the ljmp instruction. This removes the only memory access via REAL_DS (thereby allowing for the above descriptor base address hack), and also simplifies the ljmp instruction (which will still have to be emulated). Load the real-mode interrupt descriptor table register before switching to real mode, since this avoids triggering an EXCEPTION_NMI and corresponding VM exit. This reduces the time taken by prot_to_real under KVM by around 65%. Signed-off-by: Michael Brown <mcb30@ipxe.org>		10 gadus atpakaļ
contrib	[errdb] Strip platform error code for non-platform-generated errors	11 gadus atpakaļ
src	[librm] Speed up protected-to-real mode transition under KVM	10 gadus atpakaļ
COPYING	Initial revision	19 gadus atpakaļ
COPYRIGHTS	[build] Rename gPXE to iPXE	14 gadus atpakaļ
README	[doc] Re-add README file	14 gadus atpakaļ

iPXE README File

Quick start guide:

   cd src
   make

For any more detailed instructions, see http://ipxe.org