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.
Best regards Heinrich
