From: Andrew Jones <ajones@ventanamicro.com>
To: Yong-Xuan Wang <yongxuan.wang@sifive.com>
Cc: linux-riscv@lists.infradead.org, kvm-riscv@lists.infradead.org,
kvm@vger.kernel.org, will@kernel.org,
julien.thierry.kdev@gmail.com, apatel@ventanamicro.com,
greentime.hu@sifive.com, vincent.chen@sifive.com
Subject: Re: [kvmtool PATCH v2 1/1] riscv: Fix the hart bit setting of AIA
Date: Wed, 15 May 2024 16:44:27 +0200 [thread overview]
Message-ID: <20240515-354702b661f7e6351b92cb21@orel> (raw)
In-Reply-To: <20240515091902.28368-1-yongxuan.wang@sifive.com>
On Wed, May 15, 2024 at 05:19:02PM 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.wang@sifive.com/t/
>
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@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
>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
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prev parent reply other threads:[~2024-05-15 14:44 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-15 9:19 [kvmtool PATCH v2 1/1] riscv: Fix the hart bit setting of AIA Yong-Xuan Wang
2024-05-15 14:44 ` Andrew Jones [this message]
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