Re: [PATCH 17/44] KVM: arm64: Do arm/arch initialiation without bouncing through kvm_init()
From: Sean Christopherson <seanjc@google.com>
Date: 2022-11-03 15:30:57
Also in:
kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-mips, linux-riscv, linux-s390, lkml
On Thu, Nov 03, 2022, Philippe Mathieu-Daudé wrote:
Hi Sean, On 3/11/22 00:18, Sean Christopherson wrote:quoted
Move arm/arch specific initialization directly in arm's module_init(), now called kvm_arm_init(), instead of bouncing through kvm_init() to reach kvm_arch_init(). Invoking kvm_arch_init() is the very first action performed by kvm_init(), i.e. this is a glorified nop. Making kvm_arch_init() a nop will allow dropping it entirely once all other architectures follow suit. No functional change intended. Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/arm64/kvm/arm.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-)quoted
/* NOP: Compiling as a module not supported */ void kvm_arch_exit(void) { - kvm_unregister_perf_callbacks();Doesn't this belong to the previous patch?
No, but the above changelog is a lie, there is very much a functional change here.
The goal of the previous patch is to fix the error paths in kvm_arch_init(), a.k.a.
kvm_arm_init(). After fixing kvm_arch_init(), there are still bugs in the sequence
as a whole because kvm_arch_exit() doesn't unwind other state, e.g. kvm_arch_exit()
should really look something like:
void kvm_arch_exit(void)
{
teardown_subsystems();
if (!is_kernel_in_hyp_mode())
teardown_hyp_mode();
kvm_arm_vmid_alloc_free();
if (is_protected_kvm_enabled())
???
}
Becuase although the comment "NOP: Compiling as a module not supported" is correct
about KVM ARM always having to be built into the kernel, kvm_arch_exit() can still
be called if a later stage of kvm_init() fails.
But rather than add a patch to fix kvm_arch_exit(), I chose to fix the bug by
moving code out of kvm_arch_init() so that the unwind sequence established in the
previous patch could be reused.
Except I managed to forget those details when writing the changelog. The changelog
should instead be:
KVM: arm64: Do arm/arch initialization without bouncing through kvm_init()
Do arm/arch specific initialization directly in arm's module_init(), now
called kvm_arm_init(), instead of bouncing through kvm_init() to reach
kvm_arch_init(). Invoking kvm_arch_init() is the very first action
performed by kvm_init(), so from a initialization perspective this is a
glorified nop.
Avoiding kvm_arch_init() also fixes a mostly benign bug as kvm_arch_exit()
doesn't properly unwind if a later stage of kvm_init() fails. While the
soon-to-be-deleted comment about compiling as a module being unsupported
is correct, kvm_arch_exit() can still be called by kvm_init() if any step
after the call to kvm_arch_init() succeeds.
Add a FIXME to call out that pKVM initialization isn't unwound if
kvm_init() fails, which is a pre-existing problem inherited from
kvm_arch_exit().
Making kvm_arch_init() a nop will also allow dropping kvm_arch_init() and
kvm_arch_exit() entirely once all other architectures follow suit.