On Thu, Jun 29, 2023 at 12:24 AM Huacai Chen chenhuacai@kernel.org wrote:
Hi, Zhao,
On Thu, Jun 29, 2023 at 8:07 AM Yu Zhao yuzhao@google.com wrote:
On Mon, Jun 26, 2023 at 6:33 AM Paolo Bonzini pbonzini@redhat.com wrote:
On Mon, Jun 26, 2023 at 9:59 AM Huacai Chen chenhuacai@loongson.cn wrote:
After commit 45c7e8af4a5e3f0bea4ac209 ("MIPS: Remove KVM_TE support") we get a NULL pointer dereference when creating a KVM guest:
To be honest, a bug that needed 2 years to be reproduced is probably a sign that KVM/MIPS has no users. Any objections to removing it altogether?
ACK:
It's still broken after this patch [1]. The most well-tested MIPS distros, i.e., Debian/OpenWrt, have CONFIG_KVM=n. (The latter doesn't even provide the QEMU package on MIPS.)
Burden on QEMU dev. There is no guarantee that QEMU would work with KVM even if we could fix the kernel -- it actually does not until v8.0 [1], which is by luck:
commit a844873512400fae6bed9e87694dc96ff2f15f39 Author: Paolo Bonzini pbonzini@redhat.com Date: Sun Dec 18 01:06:45 2022 +0100
mips: Remove support for trap and emulate KVM This support was limited to the Malta board, drop it. I do not have a machine that can run VZ KVM, so I am assuming that it works for -M malta as well.(The latest Debian stable only ships v7.2.)
My testbed is Loongson-3A4000 host + Loongson-3A4000 guest + Qemu8.0, both TCG and KVM works.
I tried TCG too, as reported in the link above, and had no luck.
Some thoughts: 1, I think your host is malta, but you cannot use a malta host to boot a Loongson guest, at least their kernels use different page sizes.
Good to know. Thanks.
2, commit a844873512400fae6bed9e87694dc96f remove the TE KVM, so if you are trying VZ KVM (but it seems you are using TE KVM), it can break nothing.
I fully understand :) I was trying to point out that QEMU/KVM had been broken for over 2 years -- neither TE (removed from KVM) nor VZ works with 7.2, which is probably why you used 8.0 too -- until that commit *accidentally* fixed VZ (it was supposed to be a cleanup, not a fix).