[kvmtool PATCH v2 1/1] riscv: Fix the hart bit setting of AIA
Yong-Xuan Wang
yongxuan.wang at sifive.com
Wed May 15 02:19:02 PDT 2024
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@sifive.com/t/
Signed-off-by: Yong-Xuan Wang <yongxuan.wang at sifive.com>
---
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
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