Can't use graphics=vnc on TDVM
#202
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Thank you for reporting us your feedback! The internal ticket has been created: https://warthogs.atlassian.net/browse/PEK-1049.
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a minor correction, the para for vnc is: |
rpedgeco
pushed a commit
to intel/tdx
that referenced
this issue
Jan 25, 2025
…or TDs
Add a method to ignore requests to update CPU dirty logging for TDs, as
basic TDX does not support the PML feature, and KVM TDX does not allocate
or flush PML buffers for TDs.
Do not invoke vmx_update_cpu_dirty_logging() for TDs, and doing so would
cause a NULL pointer access error.
This is to fix the issue first reported in [1], where QEMU attaches an
emulated VGA device to a TD, resulting in a "kernel NULL pointer
dereference" in the host.
In QEMU, vga_common_init() sets the vram memory region to have a
dirty_log_mask with bit DIRTY_MEMORY_VGA.
pci_cirrus_vga_realize
vga_common_init
vga_dirty_log_start
memory_region_set_log
mr->dirty_log_mask = 1 << DIRTY_MEMORY_VGA;
QEMU's KVM acceleration code checks if mr->dirty_log_mask is non-zero
before setting the KVM_MEM_LOG_DIRTY_PAGES flag for the corresponding
memslot (which has no flag KVM_MEM_GUEST_MEMFD) in KVM.
This causes KVM to detect that a memslot has the KVM_MEM_LOG_DIRTY_PAGES
flag and invoke kvm_mmu_update_cpu_dirty_logging() -->
vmx_update_cpu_dirty_logging() to turn on PML, leading to the NULL pointer
access error.
Reported-by: ANAND NARSHINHA PATIL <[email protected]>
Reported-by: Pedro Principeza <[email protected]>
Reported-by: Farrah Chen <[email protected]>
Closes: canonical/tdx#202
Link: canonical/tdx#202 [1]
Signed-off-by: Yan Zhao <[email protected]>
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[Bug]
If a TDVM is created using libvirt, and it contains the VNC graphics setup as:
<graphics type="vnc"> <listen type="socket"></listen> </graphics>The VM itself crashes, and the following entries are seen in the logs:
2024-07-11T09:19:19.469114Z qemu-system-x86_64: Failed to get registers: Input/output error 2024-07-11 09:19:19.853+0000: shutting down, reason=crashed[Repro Steps]
vnc. Example here [0].[Expectation]
VNC should not fail with TDX, unless there is a full statement outlining so.
[0] https://paste.ubuntu.com/p/7p3mVG8Qwy/
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