| Message ID | 20200131155655.49812-1-cascardo@canonical.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86/kvm: do not setup pv tlb flush when not paravirtualized | expand |
Thadeu Lima de Souza Cascardo <cascardo@canonical.com> writes: > kvm_setup_pv_tlb_flush will waste memory and print a misguiding message > when KVM paravirtualization is not available. > > Intel SDM says that the when cpuid is used with EAX higher than the > maximum supported value for basic of extended function, the data for the > highest supported basic function will be returned. > > So, in some systems, kvm_arch_para_features will return bogus data, > causing kvm_setup_pv_tlb_flush to detect support for pv tlb flush. > > Testing for kvm_para_available will work as it checks for the hypervisor > signature. > > Besides, when the "nopv" command line parameter is used, it should not > continue as well, as kvm_guest_init will no be called in that case. > > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> > --- > arch/x86/kernel/kvm.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 81045aabb6f4..d817f255aed8 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -736,6 +736,9 @@ static __init int kvm_setup_pv_tlb_flush(void) > { > int cpu; > > + if (!kvm_para_available() || nopv) > + return 0; > + > if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && > !kvm_para_has_hint(KVM_HINTS_REALTIME) && > kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { The patch will fix the immediate issue, but why kvm_setup_pv_tlb_flush() is just an arch_initcall() which will be executed regardless of the fact if we are running on KVM or not? In Hyper-V we setup PV TLB flush from ms_hyperv_init_platform() -- which only happens if Hyper-V platform was detected. Why don't we do it from kvm_init_platform() in KVM?
On Mon, Feb 03, 2020 at 10:59:10AM +0100, Vitaly Kuznetsov wrote: > Thadeu Lima de Souza Cascardo <cascardo@canonical.com> writes: > > > kvm_setup_pv_tlb_flush will waste memory and print a misguiding message > > when KVM paravirtualization is not available. > > > > Intel SDM says that the when cpuid is used with EAX higher than the > > maximum supported value for basic of extended function, the data for the > > highest supported basic function will be returned. > > > > So, in some systems, kvm_arch_para_features will return bogus data, > > causing kvm_setup_pv_tlb_flush to detect support for pv tlb flush. > > > > Testing for kvm_para_available will work as it checks for the hypervisor > > signature. > > > > Besides, when the "nopv" command line parameter is used, it should not > > continue as well, as kvm_guest_init will no be called in that case. > > > > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> > > --- > > arch/x86/kernel/kvm.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > > index 81045aabb6f4..d817f255aed8 100644 > > --- a/arch/x86/kernel/kvm.c > > +++ b/arch/x86/kernel/kvm.c > > @@ -736,6 +736,9 @@ static __init int kvm_setup_pv_tlb_flush(void) > > { > > int cpu; > > > > + if (!kvm_para_available() || nopv) > > + return 0; > > + > > if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && > > !kvm_para_has_hint(KVM_HINTS_REALTIME) && > > kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { > > The patch will fix the immediate issue, but why kvm_setup_pv_tlb_flush() > is just an arch_initcall() which will be executed regardless of the fact > if we are running on KVM or not? > > In Hyper-V we setup PV TLB flush from ms_hyperv_init_platform() -- which > only happens if Hyper-V platform was detected. Why don't we do it from > kvm_init_platform() in KVM? > > -- > Vitaly > Because we can't call the allocator that early. Also, see the thread where this was "decided", the v6 of the original patch: https://lore.kernel.org/kvm/20171129162118.GA10661@flask/ Regards. Cascardo.
On Mon, 3 Feb 2020 at 18:31, Thadeu Lima de Souza Cascardo <cascardo@canonical.com> wrote: > > On Mon, Feb 03, 2020 at 10:59:10AM +0100, Vitaly Kuznetsov wrote: > > Thadeu Lima de Souza Cascardo <cascardo@canonical.com> writes: > > > > > kvm_setup_pv_tlb_flush will waste memory and print a misguiding message > > > when KVM paravirtualization is not available. > > > > > > Intel SDM says that the when cpuid is used with EAX higher than the > > > maximum supported value for basic of extended function, the data for the > > > highest supported basic function will be returned. > > > > > > So, in some systems, kvm_arch_para_features will return bogus data, > > > causing kvm_setup_pv_tlb_flush to detect support for pv tlb flush. > > > > > > Testing for kvm_para_available will work as it checks for the hypervisor > > > signature. > > > > > > Besides, when the "nopv" command line parameter is used, it should not > > > continue as well, as kvm_guest_init will no be called in that case. > > > > > > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> > > > --- > > > arch/x86/kernel/kvm.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > > > index 81045aabb6f4..d817f255aed8 100644 > > > --- a/arch/x86/kernel/kvm.c > > > +++ b/arch/x86/kernel/kvm.c > > > @@ -736,6 +736,9 @@ static __init int kvm_setup_pv_tlb_flush(void) > > > { > > > int cpu; > > > > > > + if (!kvm_para_available() || nopv) > > > + return 0; > > > + > > > if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && > > > !kvm_para_has_hint(KVM_HINTS_REALTIME) && > > > kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { > > > > The patch will fix the immediate issue, but why kvm_setup_pv_tlb_flush() > > is just an arch_initcall() which will be executed regardless of the fact > > if we are running on KVM or not? > > > > In Hyper-V we setup PV TLB flush from ms_hyperv_init_platform() -- which > > only happens if Hyper-V platform was detected. Why don't we do it from > > kvm_init_platform() in KVM? > > > > -- > > Vitaly > > > > Because we can't call the allocator that early. > > Also, see the thread where this was "decided", the v6 of the original patch: > > https://lore.kernel.org/kvm/20171129162118.GA10661@flask/ A little change to this function. https://lore.kernel.org/kvm/CANRm+CwK0Cg45mktda9Yz9fsjPCvtuB8O+fma5L3tV725ki1qw@mail.gmail.com Testing is a great appreciated. (Still in vacation) Wanpeng
Thadeu Lima de Souza Cascardo <cascardo@canonical.com> writes: > On Mon, Feb 03, 2020 at 10:59:10AM +0100, Vitaly Kuznetsov wrote: >> Thadeu Lima de Souza Cascardo <cascardo@canonical.com> writes: >> >> > kvm_setup_pv_tlb_flush will waste memory and print a misguiding message >> > when KVM paravirtualization is not available. >> > >> > Intel SDM says that the when cpuid is used with EAX higher than the >> > maximum supported value for basic of extended function, the data for the >> > highest supported basic function will be returned. >> > >> > So, in some systems, kvm_arch_para_features will return bogus data, >> > causing kvm_setup_pv_tlb_flush to detect support for pv tlb flush. >> > >> > Testing for kvm_para_available will work as it checks for the hypervisor >> > signature. >> > >> > Besides, when the "nopv" command line parameter is used, it should not >> > continue as well, as kvm_guest_init will no be called in that case. >> > >> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> >> > --- >> > arch/x86/kernel/kvm.c | 3 +++ >> > 1 file changed, 3 insertions(+) >> > >> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c >> > index 81045aabb6f4..d817f255aed8 100644 >> > --- a/arch/x86/kernel/kvm.c >> > +++ b/arch/x86/kernel/kvm.c >> > @@ -736,6 +736,9 @@ static __init int kvm_setup_pv_tlb_flush(void) >> > { >> > int cpu; >> > >> > + if (!kvm_para_available() || nopv) >> > + return 0; >> > + >> > if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && >> > !kvm_para_has_hint(KVM_HINTS_REALTIME) && >> > kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { >> >> The patch will fix the immediate issue, but why kvm_setup_pv_tlb_flush() >> is just an arch_initcall() which will be executed regardless of the fact >> if we are running on KVM or not? >> >> In Hyper-V we setup PV TLB flush from ms_hyperv_init_platform() -- which >> only happens if Hyper-V platform was detected. Why don't we do it from >> kvm_init_platform() in KVM? >> >> -- >> Vitaly >> > > Because we can't call the allocator that early. > > Also, see the thread where this was "decided", the v6 of the original patch: > > https://lore.kernel.org/kvm/20171129162118.GA10661@flask/ Ok, I see, it's basically about what we prioritize: shorter boot time vs smaller memory footprint. I'd personally vote for the former but the opposite opinion is equally valid. Let's preserve the status quo.
On 31/01/20 16:56, Thadeu Lima de Souza Cascardo wrote: > kvm_setup_pv_tlb_flush will waste memory and print a misguiding message > when KVM paravirtualization is not available. > > Intel SDM says that the when cpuid is used with EAX higher than the > maximum supported value for basic of extended function, the data for the > highest supported basic function will be returned. > > So, in some systems, kvm_arch_para_features will return bogus data, > causing kvm_setup_pv_tlb_flush to detect support for pv tlb flush. > > Testing for kvm_para_available will work as it checks for the hypervisor > signature. > > Besides, when the "nopv" command line parameter is used, it should not > continue as well, as kvm_guest_init will no be called in that case. > > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> > --- > arch/x86/kernel/kvm.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 81045aabb6f4..d817f255aed8 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -736,6 +736,9 @@ static __init int kvm_setup_pv_tlb_flush(void) > { > int cpu; > > + if (!kvm_para_available() || nopv) > + return 0; > + > if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && > !kvm_para_has_hint(KVM_HINTS_REALTIME) && > kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { > Queued, thanks. Paolo
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 81045aabb6f4..d817f255aed8 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -736,6 +736,9 @@ static __init int kvm_setup_pv_tlb_flush(void) { int cpu; + if (!kvm_para_available() || nopv) + return 0; + if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && !kvm_para_has_hint(KVM_HINTS_REALTIME) && kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
kvm_setup_pv_tlb_flush will waste memory and print a misguiding message when KVM paravirtualization is not available. Intel SDM says that the when cpuid is used with EAX higher than the maximum supported value for basic of extended function, the data for the highest supported basic function will be returned. So, in some systems, kvm_arch_para_features will return bogus data, causing kvm_setup_pv_tlb_flush to detect support for pv tlb flush. Testing for kvm_para_available will work as it checks for the hypervisor signature. Besides, when the "nopv" command line parameter is used, it should not continue as well, as kvm_guest_init will no be called in that case. Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> --- arch/x86/kernel/kvm.c | 3 +++ 1 file changed, 3 insertions(+)