On Fri, Jul 28, 2023 at 04:01:50PM +0800, Qian Wen wrote:
> Date: Fri, 28 Jul 2023 16:01:50 +0800
> From: Qian Wen <[email protected]>
> Subject: [PATCH] target/i386: Avoid cpu number overflow in legacy topology
> X-Mailer: git-send-email 2.25.1
>
> The legacy topology enumerated by CPUID.1.EBX[23:16] is defined in SDM
> Vol2:
>
> Bits 23-16: Maximum number of addressable IDs for logical processors in
> this physical package.
>
> To avoid data overflow, limit the max value written to EBX[23:16] to
> 255.
>
> Signed-off-by: Qian Wen <[email protected]>
> ---
> target/i386/cpu.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 1294be374ab2..70589a58b727 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -5356,6 +5356,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
> uint32_t die_offset;
> uint32_t limit;
> uint32_t signature[3];
> + uint32_t threads_per_socket;
> X86CPUTopoInfo topo_info;
>
> topo_info.dies_per_pkg = env->nr_dies;
> @@ -5397,8 +5398,18 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
> *ecx |= CPUID_EXT_OSXSAVE;
> }
> *edx = env->features[FEAT_1_EDX];
> - if (cs->nr_cores * cs->nr_threads > 1) {
> - *ebx |= (cs->nr_cores * cs->nr_threads) << 16;
> + /*
> + * The vCPU number more than 255 needs support of V2 Extended
> + * Topology enumerated by CPUID.0x1f or Extended Topology
> + * enumerated by CPUID.0x0b.
> + */
> + threads_per_socket = cs->nr_cores * cs->nr_threads;
> + if (threads_per_socket > 255) {
> + threads_per_socket = 255;
Straight encoding to 255 is good for me!
-Zhao
> + }
> +
> + if (threads_per_socket > 1) {
> + *ebx |= threads_per_socket << 16;
> *edx |= CPUID_HT;
> }
> /*
> --
> 2.25.1
>
