lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Mon, 27 Jan 2020 09:56:26 +0100 From: Vitaly Kuznetsov <vkuznets@...hat.com> To: Nick Desaulniers <nick.desaulniers@...il.com> Cc: Sean Christopherson <sean.j.christopherson@...el.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com, pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de Subject: Re: [PATCH] dynamically allocate struct cpumask Nick Desaulniers <nick.desaulniers@...il.com> writes: > This helps avoid avoid a potentially large stack allocation. > > When building with: > $ make CC=clang arch/x86/ CFLAGS=-Wframe-larger-than=1000 > The following warning is observed: > arch/x86/kernel/kvm.c:494:13: warning: stack frame size of 1064 bytes in > function 'kvm_send_ipi_mask_allbutself' [-Wframe-larger-than=] > static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, int > vector) > ^ > Debugging with: > https://github.com/ClangBuiltLinux/frame-larger-than > via: > $ python3 frame_larger_than.py arch/x86/kernel/kvm.o \ > kvm_send_ipi_mask_allbutself > points to the stack allocated `struct cpumask newmask` in > `kvm_send_ipi_mask_allbutself`. The size of a `struct cpumask` is > potentially large, as it's CONFIG_NR_CPUS divided by BITS_PER_LONG for > the target architecture. CONFIG_NR_CPUS for X86_64 can be as high as > 8192, making a single instance of a `struct cpumask` 1024 B. > > Signed-off-by: Nick Desaulniers <nick.desaulniers@...il.com> > --- > arch/x86/kernel/kvm.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 32ef1ee733b7..d41c0a0d62a2 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -494,13 +494,15 @@ static void kvm_send_ipi_mask(const struct cpumask *mask, int vector) > static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, int vector) > { > unsigned int this_cpu = smp_processor_id(); > - struct cpumask new_mask; > + struct cpumask *new_mask; > const struct cpumask *local_mask; > > - cpumask_copy(&new_mask, mask); > - cpumask_clear_cpu(this_cpu, &new_mask); > - local_mask = &new_mask; > + new_mask = kmalloc(sizeof(*new_mask), GFP_KERNEL); You could've used alloc_cpumask_var() instead, however, I think that memory allocation on this path is undesireable. We can always pre-allocate 1 cpumask variable per cpu and use it every time, e.g. we do this for Hyper-V. > + cpumask_copy(new_mask, mask); > + cpumask_clear_cpu(this_cpu, new_mask); > + local_mask = new_mask; > __send_ipi_mask(local_mask, vector); > + kfree(new_mask); > } > > /* -- Vitaly
Powered by blists - more mailing lists