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.wang@xxxxxxxxxx/t/ Signed-off-by: Yong-Xuan Wang <yongxuan.wang@xxxxxxxxxx> --- Changelog v2: - update commit message --- riscv/aia.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/riscv/aia.c b/riscv/aia.c index fe9399a8ffc1..21d9704145d0 100644 --- a/riscv/aia.c +++ b/riscv/aia.c @@ -164,7 +164,7 @@ static int aia__init(struct kvm *kvm) ret = ioctl(aia_fd, KVM_SET_DEVICE_ATTR, &aia_nr_sources_attr); if (ret) return ret; - aia_hart_bits = fls_long(kvm->nrcpus); + aia_hart_bits = fls_long(kvm->nrcpus - 1); ret = ioctl(aia_fd, KVM_SET_DEVICE_ATTR, &aia_hart_bits_attr); if (ret) return ret; -- 2.17.1
