[PATCH v2 2/6] arm64: KVM: Handle Set/Way CMOs as NOPs if FWB is present
From: Christoffer Dall <hidden>
Date: 2018-06-09 09:26:40
Also in:
kvm, kvmarm
On Wed, May 30, 2018 at 01:47:02PM +0100, Marc Zyngier wrote:
Set/Way handling is one of the ugliest corners of KVM. We shouldn't have to handle that, but better safe than sorry. Thankfully, FWB fixes this for us by not requiering any maintenance whatsoever, which means we don't have to emulate S/W CMOs, and don't have to track VM ops either.
I tiny bit of rationale here would have been nice. As I understand it, if we're presenting the guest with a fully coherent system, there should never be a need to invalidate anything, because the guest will always see the most recent value no matter how it sings and dances, right?
quoted hunk ↗ jump to hunk
We still have to trap S/W though, if only to prevent the guest from doing something bad. Signed-off-by: Marc Zyngier <redacted> --- arch/arm64/kvm/sys_regs.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 6e3b969391fd..9a740f159245 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c@@ -195,7 +195,13 @@ static bool access_dcsw(struct kvm_vcpu *vcpu, if (!p->is_write) return read_from_write_only(vcpu, p, r); - kvm_set_way_flush(vcpu); + /* + * Only track S/W ops if we don't have FWB. It still indicates + * that the guest is a bit broken... + */
Is it strictly true that the guest is broken if it does any form of S/W ops? Does the guest actually know that it's running on a fully coherent system, or is the argument that no software, ever, should do S/W, even for reboot etc.? I think this should have slightly more info, or that part of the comment should just be dropped, to avoid misleading future readers who don't have the full picture.
+ if (!cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) + kvm_set_way_flush(vcpu); + return true; } -- 2.17.1
Besides the usual nits on commentary: Reviewed-by: Christoffer Dall <redacted>