On Wed, May 15, 2024 at 05:11:28PM GMT, Yong-Xuan Wang wrote: > In AIA spec, each hart (or each hart within a group) has a unique hart > number to locate the memory pages of interrupt files in the address > space. The number of bits required to represent any hart number is equal > to ceil(log2(hmax + 1)), where hmax is the largest hart number among > groups. > > However, if the largest hart number among groups is a power of 2, QEMU > will pass an inaccurate hart-index-bit setting to Linux. For example, when > the guest OS has 4 harts, only ceil(log2(3 + 1)) = 2 bits are sufficient > to represent 4 harts, but we passes 3 to Linux. The code needs to be > updated to ensure accurate hart-index-bit settings. > > Additionally, a Linux patch[1] is necessary to correctly recover the hart > index when the guest OS has only 1 hart, where the hart-index-bit is 0. > > [1] > https://lore.kernel.org/lkml/20240415064905.25184-1-yongxuan.w...@sifive.com/t/ > > Signed-off-by: Yong-Xuan Wang <yongxuan.w...@sifive.com> > --- > Changelog > v2: > - update commit message > --- > target/riscv/kvm/kvm-cpu.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c > index 473416649fda..235e2cdaca1a 100644 > --- a/target/riscv/kvm/kvm-cpu.c > +++ b/target/riscv/kvm/kvm-cpu.c > @@ -1777,7 +1777,14 @@ void kvm_riscv_aia_create(MachineState *machine, > uint64_t group_shift, > } > } > > - hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1; > + > + if (max_hart_per_socket > 1) { > + max_hart_per_socket--; > + hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1; > + } else { > + hart_bits = 0; > + } > + > ret = kvm_device_access(aia_fd, KVM_DEV_RISCV_AIA_GRP_CONFIG, > KVM_DEV_RISCV_AIA_CONFIG_HART_BITS, > &hart_bits, true, NULL); > -- > 2.17.1 >
Reviewed-by: Andrew Jones <ajo...@ventanamicro.com>
