Re: [PATCH] x86: cpu: fixup number of addressable IDs for processor cores in the physical package

[Zhao Liu <zhao1.liu@intel.com>]

Hi Chuang,

On Mon, May 27, 2024 at 11:13:33AM +0800, Chuang Xu wrote:
> Date: Mon, 27 May 2024 11:13:33 +0800
> From: Chuang Xu <xuchuangxclwt@bytedance.com>
> Subject: [PATCH] x86: cpu: fixup number of addressable IDs for processor
>  cores in the physical package

According to the usual practice of QEMU commits, people tend to use
"i386/cpu" as the subject prefix, which indicates the code path.

> X-Mailer: git-send-email 2.24.3 (Apple Git-128)
> 
> When QEMU is started with:
> -cpu host,host-cache-info=on,l3-cache=off \

Just a discussion, "l3-cache=off" doesn't work in host cache pssthu
case, do you have a specific need that you don't want to see l3 cache?

> -smp 2,sockets=1,dies=1,cores=1,threads=2
> Guest can't acquire maximum number of addressable IDs for processor cores in
> the physical package from CPUID[04H].
> 
> This bug was introduced in commit d7caf13b5fcf742e5680c1d3448ba070fc811644.
> Fix it by changing the judgement condition to a >= 1.

Pls add a "Fixes" tag like:

Fixes: d7caf13b5fcf ("x86: cpu: fixup number of addressable IDs for logical processors sharing cache")

Since this is a historical issue that deserves to be ported to the
stable branch, you can cc stable list by:

Cc: qemu-stable@nongnu.org

> Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com>

As the patch sender, it's better to put your signature on the last line.
;-)

> Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com>
> Signed-off-by: Yipeng Yin <yinyipeng@bytedance.com>
> ---
>  target/i386/cpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index cd16cb893d..0369c01153 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6097,7 +6097,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>              if (*eax & 31) {
>                  int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14);
>                  int vcpus_per_socket = cs->nr_cores * cs->nr_threads;
> -                if (cs->nr_cores > 1) {
> +                if (cs->nr_cores >= 1) {

Like Igor suggested, this condition could be removed since cs->nr_cores can't
be 0.

>                      *eax &= ~0xFC000000;
>                      *eax |= (pow2ceil(cs->nr_cores) - 1) << 26;
>                  }

...the code is outdated, pls rebase on the latest master branch.

Regards,
Zhao