linux-kernel - Re: [PATCH 01/11] Add shared memory hypercall to PV Linux guest.

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Date:	Mon, 02 Nov 2009 14:18:54 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/11] Add shared memory hypercall to PV Linux guest.

On 11/01/2009 01:56 PM, Gleb Natapov wrote:
> Add hypercall that allows guest and host to setup per cpu shared
> memory.
>
>    

Better to set this up as an MSR (with bit zero enabling, bits 1-5 
features, and 64-byte alignment).  This allows auto-reset on INIT and 
live migration using the existing MSR save/restore infrastructure.

>   arch/x86/include/asm/kvm_host.h |    3 +
>   arch/x86/include/asm/kvm_para.h |   11 +++++
>   arch/x86/kernel/kvm.c           |   82 +++++++++++++++++++++++++++++++++++++++
>   arch/x86/kernel/setup.c         |    1 +
>   arch/x86/kernel/smpboot.c       |    3 +
>   arch/x86/kvm/x86.c              |   70 +++++++++++++++++++++++++++++++++
>   include/linux/kvm.h             |    1 +
>   include/linux/kvm_para.h        |    4 ++
>   8 files changed, 175 insertions(+), 0 deletions(-)
>    

Please separate into guest and host patches.

> +#define KVM_PV_SHM_VERSION 1
>    

versions = bad, feature bits = good

> +
> +#define KVM_PV_SHM_FEATURES_ASYNC_PF		(1<<  0)
> +
> +struct kvm_vcpu_pv_shm {
> +	__u64 features;
> +	__u64 reason;
> +	__u64 param;
> +};
> +
>    

Some documentation for this?

Also, the name should reflect the pv pagefault use.  For other uses we 
can register other areas.

>   #define MMU_QUEUE_SIZE 1024
>
> @@ -37,6 +41,7 @@ struct kvm_para_state {
>   };
>
>   static DEFINE_PER_CPU(struct kvm_para_state, para_state);
> +static DEFINE_PER_CPU(struct kvm_vcpu_pv_shm *, kvm_vcpu_pv_shm);
>    

Easier to put the entire structure here, not a pointer.

> +
> +static int kvm_pv_reboot_notify(struct notifier_block *nb,
> +				unsigned long code, void *unused)
> +{
> +	if (code == SYS_RESTART)
> +		on_each_cpu(kvm_pv_unregister_shm, NULL, 1);
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block kvm_pv_reboot_nb = {
> +        .notifier_call = kvm_pv_reboot_notify,
> +};
>    

Is this called on kexec, or do we need another hook?

> +static int kvm_pv_setup_shm(struct kvm_vcpu *vcpu, unsigned long gpa,
> +			    unsigned long size, unsigned long version,
> +			    unsigned long *ret)
> +{
> +	addr = gfn_to_hva(vcpu->kvm, gfn);
> +	if (kvm_is_error_hva(addr))
> +		return -EFAULT;
> +
> +	/* pin page with pv shared memory */
> +	down_read(&mm->mmap_sem);
> +	r = get_user_pages(current, mm, addr, 1, 1, 0,&vcpu->arch.pv_shm_page,
> +			   NULL);
> +	up_read(&mm->mmap_sem);
>    

This fails if the memory area straddles a page boundary.  Aligning would 
solve this.  I prefer using put_user() though than a permanent 
get_user_pages().


-- 
error compiling committee.c: too many arguments to function

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