On Wed, Sep 18, 2024 at 03:49:39PM GMT, Heinrich Schuchardt wrote: > On 18.09.24 15:12, Peter Maydell wrote: > > On Wed, 18 Sept 2024 at 14:06, Heinrich Schuchardt > > <heinrich.schuchardt@xxxxxxxxxxxxx> wrote: > > > Thanks Peter for looking into this. > > > > > > QEMU's cpu_synchronize_all_post_init() and > > > do_kvm_cpu_synchronize_post_reset() both end up in > > > kvm_arch_put_registers() and that is long after Linux > > > kvm_arch_vcpu_create() has been setting some FPU state. See the output > > > below. > > > > > > kvm_arch_put_registers() copies the CSRs by calling > > > kvm_riscv_put_regs_csr(). Here we can find: > > > > > > KVM_RISCV_SET_CSR(cs, env, sstatus, env->mstatus); > > > > > > This call enables or disables the FPU according to the value of > > > env->mstatus. > > > > > > So we need to set the desired state of the floating point unit in QEMU. > > > And this is what the current patch does both for TCG and KVM. > > > > If it does this for both TCG and KVM then I don't understand > > this bit from the commit message: > > > > # Without this patch EDK II with TLS enabled crashes when hitting the first > > # floating point instruction while running QEMU with --accel kvm and runs > > # fine with --accel tcg. > > > > Shouldn't this guest crash the same way with both KVM and TCG without > > this patch, because the FPU state is the same for both? > > > > -- PMM > > By default `qemu-system-riscv64 --accel tcg` runs OpenSBI as firmware which > enables the FPU. > > If you would choose a different SBI implementation which does not enable the > FPU you could experience the same crash. > Thanks Heinrich, I had also forgotten that distinction. So the last question is whether or not we want to reset mstatus.FS to 1 instead of 3, as is done in this patch. Thanks, drew
