[Bug 213781] KVM: x86/svm: The guest (#vcpu>1) can't boot up with QEMU "-overcommit cpu-pm=on"

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=213781

Like Xu (like.xu.linux@gmail.com) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Kernel Version|5.14.0-rc1+                 |5.19.0-rc1+

--- Comment #4 from Like Xu (like.xu.linux@gmail.com) ---
The issue still exits on the AMD after we revert the commit in 31c25585695a.

Just confirmed that it's caused by non-atomic accesses to memslot:
- __do_insn_fetch_bytes() from the prot32 code page #NPF;
- kvm_vm_ioctl_set_memory_region() from user space;

Considering the expected result [selftests::test_zero_memory_regions on x86_64]
is that the guest will trigger an internal KVM error due to the initial code
fetch encountering a non-existent memslot and resulting in an emulation
failure.

More similar cases will gradually emerge. I'm not sure if KVM has documentation
pointing out this restriction on memslot updates (fix one application QEMU may
be one-sided), or any need to add something unwise like check
gfn_to_memslot(kvm, gpa_to_gfn(cr2_or_gpa)) in the x86_emulate_instruction().

Any other suggestions ?

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