Messages in this thread | | | Subject | Re: [PATCH v6 1/6] arm64/kvm: preserve host HCR_EL2 value | From | Amit Daniel Kachhap <> | Date | Fri, 1 Mar 2019 11:26:05 +0530 |
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Hi,
On 2/21/19 9:19 PM, Dave Martin wrote: > On Tue, Feb 19, 2019 at 02:54:26PM +0530, Amit Daniel Kachhap wrote: >> From: Mark Rutland <mark.rutland@arm.com> >> >> When restoring HCR_EL2 for the host, KVM uses HCR_HOST_VHE_FLAGS, which >> is a constant value. This works today, as the host HCR_EL2 value is >> always the same, but this will get in the way of supporting extensions >> that require HCR_EL2 bits to be set conditionally for the host. >> >> To allow such features to work without KVM having to explicitly handle >> every possible host feature combination, this patch has KVM save/restore >> for the host HCR when switching to/from a guest HCR. The saving of the >> register is done once during cpu hypervisor initialization state and is >> just restored after switch from guest. >> >> For fetching HCR_EL2 during kvm initialisation, a hyp call is made using >> kvm_call_hyp and is helpful in NHVE case. > > Minor nit: NVHE misspelled. This looks a bit like it's naming an arch > feature rather than a kernel implementation detail though. Maybe write > "non-VHE". yes. > >> For the hyp TLB maintenance code, __tlb_switch_to_host_vhe() is updated >> to toggle the TGE bit with a RMW sequence, as we already do in >> __tlb_switch_to_guest_vhe(). >> >> The value of hcr_el2 is now stored in struct kvm_cpu_context as both host >> and guest can now use this field in a common way. >> >> Signed-off-by: Mark Rutland <mark.rutland@arm.com> >> [Added __cpu_copy_hyp_conf, hcr_el2 field in struct kvm_cpu_context] >> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> >> Cc: Marc Zyngier <marc.zyngier@arm.com> >> Cc: Christoffer Dall <christoffer.dall@arm.com> >> Cc: kvmarm@lists.cs.columbia.edu >> --- >> arch/arm/include/asm/kvm_host.h | 2 ++ >> arch/arm64/include/asm/kvm_asm.h | 2 ++ >> arch/arm64/include/asm/kvm_emulate.h | 22 +++++++++++----------- >> arch/arm64/include/asm/kvm_host.h | 13 ++++++++++++- >> arch/arm64/include/asm/kvm_hyp.h | 2 +- >> arch/arm64/kvm/guest.c | 2 +- >> arch/arm64/kvm/hyp/switch.c | 23 +++++++++++++---------- >> arch/arm64/kvm/hyp/sysreg-sr.c | 21 ++++++++++++++++++++- >> arch/arm64/kvm/hyp/tlb.c | 6 +++++- >> virt/kvm/arm/arm.c | 1 + >> 10 files changed, 68 insertions(+), 26 deletions(-) >> >> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h >> index ca56537..05706b4 100644 >> --- a/arch/arm/include/asm/kvm_host.h >> +++ b/arch/arm/include/asm/kvm_host.h >> @@ -273,6 +273,8 @@ static inline void __cpu_init_stage2(void) >> kvm_call_hyp(__init_stage2_translation); >> } >> >> +static inline void __cpu_copy_hyp_conf(void) {} >> + >> static inline int kvm_arch_vm_ioctl_check_extension(struct kvm *kvm, long ext) >> { >> return 0; >> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h >> index f5b79e9..8acd73f 100644 >> --- a/arch/arm64/include/asm/kvm_asm.h >> +++ b/arch/arm64/include/asm/kvm_asm.h >> @@ -80,6 +80,8 @@ extern void __vgic_v3_init_lrs(void); >> >> extern u32 __kvm_get_mdcr_el2(void); >> >> +extern void __kvm_populate_host_regs(void); >> + >> /* Home-grown __this_cpu_{ptr,read} variants that always work at HYP */ >> #define __hyp_this_cpu_ptr(sym) \ >> ({ \ >> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h >> index 506386a..0dbe795 100644 >> --- a/arch/arm64/include/asm/kvm_emulate.h >> +++ b/arch/arm64/include/asm/kvm_emulate.h >> @@ -50,25 +50,25 @@ void kvm_inject_pabt32(struct kvm_vcpu *vcpu, unsigned long addr); >> >> static inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu) >> { >> - return !(vcpu->arch.hcr_el2 & HCR_RW); >> + return !(vcpu->arch.ctxt.hcr_el2 & HCR_RW); > > Putting hcr_el2 into struct kvm_cpu_context creates a lot of splatter > here, and I'm wondering whether it's really necessary. Otherwise, > we could just put the per-vcpu guest HCR_EL2 value in struct > kvm_vcpu_arch. I did like that in V4 version [1] but comments were raised that this was repetition of hcr_el2 field in 2 places and may be avoided.
[1]: https://lkml.org/lkml/2019/1/4/433 > > Is the *host* hcr_el2 value really different per-vcpu? That looks > odd. I would have thought this is fixed across the system at KVM > startup time. > > Having a single global host hcr_el2 would also avoid the need for > __kvm_populate_host_regs(): instead, we just decide what HCR_EL2 is to > be ahead of time and set a global variable that we map into Hyp. > > > Or does the host HCR_EL2 need to vary at runtime for some reason I've > missed? This patch basically makes host hcr_el2 not to use fixed values like HCR_HOST_NVHE_FLAGS/HCR_HOST_VHE_FLAGS during context switch and hence saves those values at boot time. This patch is just preparation to configure host hcr_el2 dynamically. However currently it is same for all cpus.
I suppose it is better to have host hcr_el2 as percpu to take care of heterogeneous systems. Currently even host mdcr_el2 is stored on percpu basis(arch/arm64/kvm/debug.c). > > [...] > > +void __hyp_text __kvm_populate_host_regs(void) > +{ > + struct kvm_cpu_context *host_ctxt; > + > + if (has_vhe()) > + host_ctxt = this_cpu_ptr(&kvm_host_cpu_state); > + else > + host_ctxt = __hyp_this_cpu_ptr(kvm_host_cpu_state); > > According to the comment by the definition of __hyp_this_cpu_ptr(), this > always works at Hyp. I also see other calls with no fallback > this_cpu_ptr() call like we have here. > > So, can we simply always call __hyp_this_cpu_ptr() here? Yes i missed this.
Thanks, Amit D > > (I'm not familiar with this, myself.) > > Cheers > ---Dave >
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