Hi Eric, > -----Original Message----- > From: Eric Auger <[email protected]> > Sent: 03 May 2026 08:34 > To: [email protected]; [email protected]; qemu- > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; Shameer Kolothum Thodi > <[email protected]>; [email protected] > Cc: [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected] > Subject: [PATCH v4 11/17] arm/kvm: write back modified ID regs to KVM > > External email: Use caution opening links or attachments > > > We want to give a chance to override the value of host ID regs. > In a previous patch we made sure all their values could be fetched > through kvm_get_one_reg() calls before their modification. After > their potential modification we need to make sure we write back > the values through kvm_set_one_reg() calls. > > Make sure the cpreg_list is modified with updated values and > transfer those values back to kvm. > > Signed-off-by: Eric Auger <[email protected]> > Signed-off-by: Cornelia Huck <[email protected]> > --- > target/arm/kvm.c | 59 > ++++++++++++++++++++++++++++++++++++++++- > target/arm/trace-events | 1 + > 2 files changed, 59 insertions(+), 1 deletion(-) > > diff --git a/target/arm/kvm.c b/target/arm/kvm.c > index 1a9b91bf8a..ca9a7d9439 100644 > --- a/target/arm/kvm.c > +++ b/target/arm/kvm.c > @@ -275,6 +275,21 @@ static uint32_t kvm_arm_sve_get_vls(int fd) > return vls[0] & MAKE_64BIT_MASK(0, ARM_MAX_VQ); > } > > +static int kvm_feature_idx_to_idregs_idx(int kidx) > +{ > + int op1, crm, op2; > + ARMSysRegs sysreg; > + > + op1 = kidx / 64; > + if (op1 == 2) { > + op1 = 3; > + } > + crm = (kidx % 64) / 8; > + op2 = kidx % 8; > + sysreg = ENCODE_ID_REG(3, op1, 0, crm, op2); > + return get_sysreg_idx(sysreg); > +} > + > static int idregs_idx_to_kvm_feature_idx(ARMIDRegisterIdx idx) > { > ARMSysRegs sysreg = id_register_sysreg[idx]; > @@ -1197,6 +1212,39 @@ bool kvm_arm_cpu_post_load(ARMCPU *cpu) > return true; > } > > +static void kvm_arm_writable_idregs_to_cpreg_list(ARMCPU *cpu) > +{ > + if (!cpu->writable_map) { > + return; > + } > + for (int i = 0; i < NR_ID_REG_MASKS; i++) { > + uint64_t writable_mask = cpu->writable_map->regs[i]; > + uint64_t *cpreg; > + > + if (writable_mask) { > + uint64_t previous, new; > + int idx = kvm_feature_idx_to_idregs_idx(i); > + ARM64SysReg *sysregdesc; > + uint32_t sysreg; > + > + if (idx == -1) { > + /* sysreg writable, but we don't know it */ > + continue; > + } > + sysregdesc = &arm64_id_regs[idx]; > + sysreg = sysregdesc->sysreg; > + cpreg = kvm_arm_get_cpreg_ptr(cpu, > idregs_sysreg_to_kvm_reg(sysreg)); > + previous = *cpreg; > + new = cpu->isar.idregs[idx]; > + if (previous != new) { > + *cpreg = new; > + trace_kvm_arm_writable_idregs_to_cpreg_list(sysregdesc->name, > + previous, new); > + } > + } > + } > +} > + > void kvm_arm_reset_vcpu(ARMCPU *cpu) > { > int ret; > @@ -2148,7 +2196,16 @@ int kvm_arch_init_vcpu(CPUState *cs) > } > cpu->mp_affinity = mpidr & ARM64_AFFINITY_MASK; > > - return kvm_arm_init_cpreg_list(cpu); > + ret = kvm_arm_init_cpreg_list(cpu); > + if (ret) { > + return ret; > + } > + /* overwrite writable ID regs with their updated property values */ > + kvm_arm_writable_idregs_to_cpreg_list(cpu); > + > + write_list_to_kvmstate(cpu, KVM_PUT_FULL_STATE);
KVM may hide registers based on ID register fields when features are disabled. Updating writable ID registers after KVM_GET_REG_LIST can result in a mismatched register list and failures when setting registers. This was reported on v3: https://lore.kernel.org/qemu-devel/[email protected]/ Is this fixed someway in this series? I am not sure. I have faced the same issue on NV platforms as well. Thanks, Shameer
