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When SEV is enabled, every debug message printed by OVMF to the QEMU debug port traps from the guest to QEMU character by character because "REP OUTSB" cannot be used by IoWriteFifo8. Furthermore, when OVMF is built with the DEBUG_VERBOSE bit (value 0x00400000) enabled in "gEfiMdePkgTokenSpaceGuid.PcdDebugPrintErrorLevel", then the OvmfPkg/IoMmuDxe driver, and the OvmfPkg/Library/BaseMemEncryptSevLib library instance that is built into it, produce a huge amount of log messages. Therefore, in SEV guests, the boot time impact is huge (about 45 seconds _additional_ time spent writing to the debug port). While these messages are very useful for analyzing guest behavior, most of the time the user won't be capturing the OVMF debug log. In fact libvirt does not provide a method for configuring log capture; users that wish to do this (or are instructed to do this) have to resort to <qemu:arg>. The debug console device provides a handy detection mechanism; when read, it returns 0xE9 (which is very much unlike the 0xFF that is returned by an unused port). Use it to skip the possibly expensive OUT instructions when the debug I/O port isn't plugged anywhere. For SEC, the debug port has to be read before each full message. However: - if the debug port is available, then reading one byte before writing a full message isn't tragic, especially because SEC doesn't print many messages - if the debug port is not available, then reading one byte instead of writing a full message is still a win. Contributed-under: TianoCore Contribution Agreement 1.0 Cc: Laszlo Ersek <lersek@redhat.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Jordan Justen (Intel address) <jordan.l.justen@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Tested-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
EDK II Project
A modern, feature-rich, cross-platform firmware development environment for the UEFI and PI specifications from www.uefi.org.
Contributions to the EDK II open source project are covered by the TianoCore Contribution Agreement 1.1
The majority of the content in the EDK II open source project uses a BSD 2-Clause License. The EDK II open source project contains the following components that are covered by additional licenses:
- AppPkg/Applications/Python/Python-2.7.2/Tools/pybench
- AppPkg/Applications/Python/Python-2.7.2
- AppPkg/Applications/Python/Python-2.7.10
- BaseTools/Source/C/BrotliCompress
- MdeModulePkg/Library/BrotliCustomDecompressLib
- OvmfPkg
- CryptoPkg/Library/OpensslLib/openssl
The EDK II Project is composed of packages. The maintainers for each package are listed in Maintainers.txt.