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Date:   Wed, 25 Nov 2020 10:39:46 +0000
From:   David Brazdil <dbrazdil@google.com>
To:     Marc Zyngier <maz@kernel.org>
Cc:     kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Dennis Zhou <dennis@kernel.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Quentin Perret <qperret@google.com>,
        Andrew Scull <ascull@google.com>,
        Andrew Walbran <qwandor@google.com>, kernel-team@android.com
Subject: Re: [PATCH v2 06/24] kvm: arm64: Move hyp-init params to a per-CPU
 struct
Message-ID: <20201125103946.2unmclsdfqpr3eyk@google.com>
References: <20201116204318.63987-1-dbrazdil@google.com>
 <20201116204318.63987-7-dbrazdil@google.com>
 <87lfes5f54.wl-maz@kernel.org>
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On Mon, Nov 23, 2020 at 02:20:07PM +0000, Marc Zyngier wrote:
> On Mon, 16 Nov 2020 20:43:00 +0000,
> David Brazdil <dbrazdil@google.com> wrote:
> > 
> > Once we start initializing KVM on newly booted cores before the rest of
> > the kernel, parameters to __do_hyp_init will need to be provided by EL2
> > rather than EL1. At that point it will not be possible to pass its four
> > arguments directly because PSCI_CPU_ON only supports one context
> > argument.
> > 
> > Refactor __do_hyp_init to accept its parameters in a struct. This
> > prepares the code for KVM booting cores as well as removes any limits on
> > the number of __do_hyp_init arguments.
> > 
> > Signed-off-by: David Brazdil <dbrazdil@google.com>
> > ---
> >  arch/arm64/include/asm/kvm_asm.h   |  7 +++++++
> >  arch/arm64/include/asm/kvm_hyp.h   |  4 ++++
> >  arch/arm64/kernel/asm-offsets.c    |  4 ++++
> >  arch/arm64/kvm/arm.c               | 26 ++++++++++++++------------
> >  arch/arm64/kvm/hyp/nvhe/hyp-init.S | 21 ++++++++++-----------
> >  arch/arm64/kvm/hyp/nvhe/hyp-main.c |  2 ++
> >  6 files changed, 41 insertions(+), 23 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > index 54387ccd1ab2..01904e88cead 100644
> > --- a/arch/arm64/include/asm/kvm_asm.h
> > +++ b/arch/arm64/include/asm/kvm_asm.h
> > @@ -150,6 +150,13 @@ extern void *__vhe_undefined_symbol;
> >  
> >  #endif
> >  
> > +struct kvm_nvhe_init_params {
> > +	unsigned long tpidr_el2;
> > +	unsigned long vector_hyp_va;
> > +	unsigned long stack_hyp_va;
> > +	phys_addr_t pgd_pa;
> > +};
> > +
> >  /* Translate a kernel address @ptr into its equivalent linear mapping */
> >  #define kvm_ksym_ref(ptr)						\
> >  	({								\
> > diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> > index 6b664de5ec1f..a3289071f3d8 100644
> > --- a/arch/arm64/include/asm/kvm_hyp.h
> > +++ b/arch/arm64/include/asm/kvm_hyp.h
> > @@ -15,6 +15,10 @@
> >  DECLARE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
> >  DECLARE_PER_CPU(unsigned long, kvm_hyp_vector);
> >  
> > +#ifdef __KVM_NVHE_HYPERVISOR__
> > +DECLARE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> > +#endif
> 
> I'm not sure we should bother with this #ifdefery. Having the
> declaration present at all times doesn't really hurt, since it is only
> defined in the HYP code. Cutting down on the conditionals would
> certainly help readability.
> 
> > +
> >  #define read_sysreg_elx(r,nvh,vh)					\
> >  	({								\
> >  		u64 reg;						\
> > diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> > index 7d32fc959b1a..4435ad8be938 100644
> > --- a/arch/arm64/kernel/asm-offsets.c
> > +++ b/arch/arm64/kernel/asm-offsets.c
> > @@ -110,6 +110,10 @@ int main(void)
> >    DEFINE(CPU_APGAKEYLO_EL1,	offsetof(struct kvm_cpu_context, sys_regs[APGAKEYLO_EL1]));
> >    DEFINE(HOST_CONTEXT_VCPU,	offsetof(struct kvm_cpu_context, __hyp_running_vcpu));
> >    DEFINE(HOST_DATA_CONTEXT,	offsetof(struct kvm_host_data, host_ctxt));
> > +  DEFINE(NVHE_INIT_TPIDR_EL2,	offsetof(struct kvm_nvhe_init_params, tpidr_el2));
> > +  DEFINE(NVHE_INIT_VECTOR_HYP_VA,	offsetof(struct kvm_nvhe_init_params, vector_hyp_va));
> > +  DEFINE(NVHE_INIT_STACK_HYP_VA,	offsetof(struct kvm_nvhe_init_params, stack_hyp_va));
> > +  DEFINE(NVHE_INIT_PGD_PA,	offsetof(struct kvm_nvhe_init_params, pgd_pa));
> >  #endif
> >  #ifdef CONFIG_CPU_PM
> >    DEFINE(CPU_CTX_SP,		offsetof(struct cpu_suspend_ctx, sp));
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index c0ffb019ca8b..4838556920fb 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -50,6 +50,7 @@ DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
> >  
> >  static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
> >  unsigned long kvm_arm_hyp_percpu_base[NR_CPUS];
> > +DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> >  
> >  /* The VMID used in the VTTBR */
> >  static atomic64_t kvm_vmid_gen = ATOMIC64_INIT(1);
> > @@ -1347,10 +1348,7 @@ static int kvm_map_vectors(void)
> >  
> >  static void cpu_init_hyp_mode(void)
> >  {
> > -	phys_addr_t pgd_ptr;
> > -	unsigned long hyp_stack_ptr;
> > -	unsigned long vector_ptr;
> > -	unsigned long tpidr_el2;
> > +	struct kvm_nvhe_init_params *params = this_cpu_ptr_nvhe_sym(kvm_init_params);
> >  	struct arm_smccc_res res;
> >  
> >  	/* Switch from the HYP stub to our own HYP init vector */
> > @@ -1361,13 +1359,18 @@ static void cpu_init_hyp_mode(void)
> >  	 * kernel's mapping to the linear mapping, and store it in tpidr_el2
> >  	 * so that we can use adr_l to access per-cpu variables in EL2.
> >  	 */
> > -	tpidr_el2 = (unsigned long)this_cpu_ptr_nvhe_sym(__per_cpu_start) -
> > -		    (unsigned long)kvm_ksym_ref(CHOOSE_NVHE_SYM(__per_cpu_start));
> > +	params->tpidr_el2 = (unsigned long)this_cpu_ptr_nvhe_sym(__per_cpu_start) -
> > +			    (unsigned long)kvm_ksym_ref(CHOOSE_NVHE_SYM(__per_cpu_start));
> >  
> > -	pgd_ptr = kvm_mmu_get_httbr();
> > -	hyp_stack_ptr = __this_cpu_read(kvm_arm_hyp_stack_page) + PAGE_SIZE;
> > -	hyp_stack_ptr = kern_hyp_va(hyp_stack_ptr);
> > -	vector_ptr = (unsigned long)kern_hyp_va(kvm_ksym_ref(__kvm_hyp_host_vector));
> > +	params->vector_hyp_va = (unsigned long)kern_hyp_va(kvm_ksym_ref(__kvm_hyp_host_vector));
> > +	params->stack_hyp_va = kern_hyp_va(__this_cpu_read(kvm_arm_hyp_stack_page) + PAGE_SIZE);
> > +	params->pgd_pa = kvm_mmu_get_httbr();
> 
> Note to self: rename this to kvm_mmu_get_hyp_pgd() (another AArch32-ism).
> 
> > +
> > +	/*
> > +	 * Flush the init params from the data cache because the struct will
> > +	 * be read while the MMU is off.
> > +	 */
> > +	__flush_dcache_area(params, sizeof(*params));
> 
> nit: please use kvm_flush_dcache_to_poc(), as it clearly indicates to
> which point we are flushing.

Will change, but out of curiosity - how is it different? AFAICT, it is just
an alias with a single use in __clean_dcache_guest_page:

  #define kvm_flush_dcache_to_poc(a,l)	__flush_dcache_area((a), (l))

> 
> Thanks,
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.