| Message ID | 20240603083641.97241-1-xuchuangxclwt@bytedance.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] i386/cpu: fixup number of addressable IDs for processor cores in the physical package | expand |
Hi Chuang, On Mon, Jun 03, 2024 at 04:36:41PM +0800, Chuang Xu wrote: > Date: Mon, 3 Jun 2024 16:36:41 +0800 > From: Chuang Xu <xuchuangxclwt@bytedance.com> > Subject: [PATCH v2] i386/cpu: fixup number of addressable IDs for processor > cores in the physical package > 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 \ > -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]. > > When testing Intel TDX, guest attempts to acquire extended topology from CPUID[0bH], > but because the TDX module doesn't provide the emulation of CPUID[0bH], > guest will instead acquire extended topology from CPUID[04H]. However, > due to QEMU's inaccurate emulation of CPUID[04H], one of the vcpus in 2c TDX > guest would be offline. I guess this case is based on downstream's TDX patches... Since TDX hasn't landed in QEMU yet, it's a bit ahead of the curve to elaborate on TDX-specific case. Because normal VM will also face the such cache topology error, I think it could be stated a bit more generically like: When creating a CPU topology of 1 core per package, host-cache-info only uses the Host's addressable core IDs field (CPUID.04H.EAX[bits 31-26]), resulting in a conflict (on the multicore Host) between the Guest core topology information in this field and the Guest's actual cores number. Fix it by removing the unnecessary condition to cover 1 core per package case. This is safe because cores_per_pkg will not be 0 and will be at least 1. > Fix it by removing the unnecessary condition. > > Fixes: d7caf13b5fcf742e5680c1d3448ba070fc811644 ("x86: cpu: fixup number of addressable IDs for logical processors sharing cache") 12 characters (d7caf13b5fcf) is enough. No blank line. ;-) > Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com> > Signed-off-by: Yipeng Yin <yinyipeng@bytedance.com> > Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com> > --- > target/i386/cpu.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index bc2dceb647..b68f7460db 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -6426,10 +6426,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, > if (*eax & 31) { > int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14); > > - if (cores_per_pkg > 1) { > - *eax &= ~0xFC000000; > - *eax |= max_core_ids_in_package(&topo_info) << 26; > - } > + *eax &= ~0xFC000000; > + *eax |= max_core_ids_in_package(&topo_info) << 26; > if (host_vcpus_per_cache > threads_per_pkg) { > *eax &= ~0x3FFC000; > > -- > 2.20.1 >
On 6/4/2024 5:43 PM, Zhao Liu wrote: > Hi Chuang, > > On Mon, Jun 03, 2024 at 04:36:41PM +0800, Chuang Xu wrote: >> Date: Mon, 3 Jun 2024 16:36:41 +0800 >> From: Chuang Xu <xuchuangxclwt@bytedance.com> >> Subject: [PATCH v2] i386/cpu: fixup number of addressable IDs for processor >> cores in the physical package >> 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 \ >> -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]. >> >> When testing Intel TDX, guest attempts to acquire extended topology from CPUID[0bH], >> but because the TDX module doesn't provide the emulation of CPUID[0bH], >> guest will instead acquire extended topology from CPUID[04H]. However, >> due to QEMU's inaccurate emulation of CPUID[04H], one of the vcpus in 2c TDX >> guest would be offline. > > I guess this case is based on downstream's TDX patches... Since TDX > hasn't landed in QEMU yet, it's a bit ahead of the curve to elaborate on > TDX-specific case. > > Because normal VM will also face the such cache topology error, I think > it could be stated a bit more generically like: yes. it's not TDX specific though it's found by TDX case. I think We can reproduce it by limiting the "min-level" to less than 0xb and disable "full-cpuid-auto-level". With it, CPUID leaves 0xb are not exposed to guest and guest will use leaves 0x4 to enumerate the CPU topology. > When creating a CPU topology of 1 core per package, host-cache-info only > uses the Host's addressable core IDs field (CPUID.04H.EAX[bits 31-26]), > resulting in a conflict (on the multicore Host) between the Guest core > topology information in this field and the Guest's actual cores number. > > Fix it by removing the unnecessary condition to cover 1 core per package > case. This is safe because cores_per_pkg will not be 0 and will be at > least 1. > >> Fix it by removing the unnecessary condition. >> >> Fixes: d7caf13b5fcf742e5680c1d3448ba070fc811644 ("x86: cpu: fixup number of addressable IDs for logical processors sharing cache") yeah. This is the exact commit that introduced the issue. Because it moved *eax &= ~0xFC000000; into the condition of cs->nr_cores > 1 > 12 characters (d7caf13b5fcf) is enough. No blank line. ;-) > >> Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com> >> Signed-off-by: Yipeng Yin <yinyipeng@bytedance.com> >> Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com> >> --- >> target/i386/cpu.c | 6 ++---- >> 1 file changed, 2 insertions(+), 4 deletions(-) >> >> diff --git a/target/i386/cpu.c b/target/i386/cpu.c >> index bc2dceb647..b68f7460db 100644 >> --- a/target/i386/cpu.c >> +++ b/target/i386/cpu.c >> @@ -6426,10 +6426,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, >> if (*eax & 31) { >> int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14); >> >> - if (cores_per_pkg > 1) { >> - *eax &= ~0xFC000000; >> - *eax |= max_core_ids_in_package(&topo_info) << 26; >> - } >> + *eax &= ~0xFC000000; >> + *eax |= max_core_ids_in_package(&topo_info) << 26; >> if (host_vcpus_per_cache > threads_per_pkg) { >> *eax &= ~0x3FFC000; >> >> -- >> 2.20.1 >> >
diff --git a/target/i386/cpu.c b/target/i386/cpu.c index bc2dceb647..b68f7460db 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -6426,10 +6426,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, if (*eax & 31) { int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14); - if (cores_per_pkg > 1) { - *eax &= ~0xFC000000; - *eax |= max_core_ids_in_package(&topo_info) << 26; - } + *eax &= ~0xFC000000; + *eax |= max_core_ids_in_package(&topo_info) << 26; if (host_vcpus_per_cache > threads_per_pkg) { *eax &= ~0x3FFC000;
When QEMU is started with: -cpu host,host-cache-info=on,l3-cache=off \ -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]. When testing Intel TDX, guest attempts to acquire extended topology from CPUID[0bH], but because the TDX module doesn't provide the emulation of CPUID[0bH], guest will instead acquire extended topology from CPUID[04H]. However, due to QEMU's inaccurate emulation of CPUID[04H], one of the vcpus in 2c TDX guest would be offline. Fix it by removing the unnecessary condition. Fixes: d7caf13b5fcf742e5680c1d3448ba070fc811644 ("x86: cpu: fixup number of addressable IDs for logical processors sharing cache") Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com> Signed-off-by: Yipeng Yin <yinyipeng@bytedance.com> Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com> --- target/i386/cpu.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)