Thanks for you reply, we have some hosts running with legacy kernel, difficult to upgrade, and i want to run the latest qemu. Does QEMU support running with legacy kernel(kvm) in design?
owen...@ucloud.cn From: Eduardo Habkost Date: 2019-08-21 05:23 To: Bingsong Si CC: qemu-devel Subject: Re: [Qemu-devel] [PATCH] Revert "i386: correct cpu_x86_cpuid(0xd)" On Mon, Aug 19, 2019 at 06:09:24PM +0800, Bingsong Si wrote: > This reverts commit de2e68c902f7b6e438b0fa3cfedd74a06a20704f. > > Initial value of env->xcr0 == 0, then CPUID(EAX=0xd,ECX=0).EBX == 0, after kvm > upstream commit 412a3c41, It is ok. > On host before commit 412a3c41, some legacy guest, i.e. CentOS 6, get > xstate_size == 0, will crash the guest. > > Signed-off-by: Bingsong Si <owen...@ucloud.cn> cpu_x86_cpuid() is also used by TCG, and needs to return the correct data depending on xcr0. If you want to work around a KVM bug by ignoring xcr0, it needs to be conditional on kvm_enabled(). But even if we you make this conditional on kvm_enabled(), I don't understand why QEMU would need a workaround for a KVM bug that was fixed more than 4 years ago. > --- > 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 ff65e11008..69562e21ed 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -4416,7 +4416,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, > uint32_t count, > *ecx = xsave_area_size(x86_cpu_xsave_components(cpu)); > *eax = env->features[FEAT_XSAVE_COMP_LO]; > *edx = env->features[FEAT_XSAVE_COMP_HI]; > - *ebx = xsave_area_size(env->xcr0); > + *ebx = *ecx; > } else if (count == 1) { > *eax = env->features[FEAT_XSAVE]; > } else if (count < ARRAY_SIZE(x86_ext_save_areas)) { > -- > 2.22.0 > > -- Eduardo