Re: [patch 3/5] KVM: hypercall batching

[Hollis Blanchard <hollisb@us.ibm.com>]

On Sat, 2008-02-16 at 17:09 -0500, Marcelo Tosatti wrote:
> plain text document attachment (kvm-multicall)
> Batch pte updates and tlb flushes in lazy MMU mode.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: Anthony Liguori <aliguori@us.ibm.com>
> 
> Index: kvm.paravirt/arch/x86/kernel/kvm.c
> ===================================================================
> --- kvm.paravirt.orig/arch/x86/kernel/kvm.c
> +++ kvm.paravirt/arch/x86/kernel/kvm.c
> @@ -25,6 +25,74 @@
>  #include <linux/kvm_para.h>
>  #include <linux/cpu.h>
>  #include <linux/mm.h>
> +#include <linux/hardirq.h>
> +
> +#define MAX_MULTICALL_NR (PAGE_SIZE / sizeof(struct kvm_multicall_entry))
> +
> +struct kvm_para_state {
> +	struct kvm_multicall_entry queue[MAX_MULTICALL_NR];
> +	int queue_index;
> +	enum paravirt_lazy_mode mode;
> +};
> +
> +static DEFINE_PER_CPU(struct kvm_para_state, para_state);

AFAICS there is no guarantee about page-alignment here...

> +static int kvm_hypercall_multicall(struct kvm_vcpu *vcpu, gpa_t addr, u32 nents)
> +{
> +	int i, result = 0;
> +
> +	++vcpu->stat.multicall;
> +	vcpu->stat.multicall_nr += nents;
> +
> +	for (i = 0; i < nents; i++) {
> +		struct kvm_multicall_entry mc;
> +		int ret;
> +
> +		down_read(&vcpu->kvm->slots_lock);
> +		ret = kvm_read_guest(vcpu->kvm, addr, &mc, sizeof(mc));
> +		up_read(&vcpu->kvm->slots_lock);
> +		if (ret)
> +			return -KVM_EFAULT;
> +
> +		ret = dispatch_hypercall(vcpu, mc.nr, mc.a0, mc.a1, mc.a2,
> +					    mc.a3);
> +		if (ret)
> +			result = ret;
> +		addr += sizeof(mc);
> +	}
> +	if (result < 0)
> +		return -KVM_EINVAL;
> +	return result;
> +}

... but here you're assuming that 'queue' is physically contiguous,
which is not necessarily true one you cross a page boundary.

-- 
Hollis Blanchard
IBM Linux Technology Center


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