linux-kernel - Re: [PATCH RESEND v2 15/17] KVM: selftests: Add dirty ring buffer test

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Date:   Tue, 24 Dec 2019 10:22:45 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dr David Alan Gilbert <dgilbert@...hat.com>,
        Christophe de Dinechin <dinechin@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH RESEND v2 15/17] KVM: selftests: Add dirty ring buffer
 test

On Tue, Dec 24, 2019 at 02:18:37PM +0800, Jason Wang wrote:

[...]

> > +	while (fetch != avail) {
> > +		cur = &dirty_gfns[fetch % TEST_DIRTY_RING_COUNT];
> > +		TEST_ASSERT(cur->pad == 0, "Padding is non-zero: 0x%x", cur->pad);
> > +		TEST_ASSERT(cur->slot == slot, "Slot number didn't match: "
> > +			    "%u != %u", cur->slot, slot);
> > +		TEST_ASSERT(cur->offset < num_pages, "Offset overflow: "
> > +			    "0x%llx >= 0x%llx", cur->offset, num_pages);
> > +		DEBUG("fetch 0x%x offset 0x%llx\n", fetch, cur->offset);
> > +		test_and_set_bit(cur->offset, bitmap);
> > +		fetch++;
> 
> 
> Any reason to use test_and_set_bit()? I guess set_bit() should be
> sufficient.

Yes.

> 
> 
> > +		count++;
> > +	}
> > +	WRITE_ONCE(indices->fetch_index, fetch);
> 
> 
> Is WRITE_ONCE a must here?

No.

[...]

> > +void *vcpu_map_dirty_ring(struct kvm_vm *vm, uint32_t vcpuid)
> > +{
> > +	struct vcpu *vcpu;
> > +	uint32_t size = vm->dirty_ring_size;
> > +
> > +	TEST_ASSERT(size > 0, "Should enable dirty ring first");
> > +
> > +	vcpu = vcpu_find(vm, vcpuid);
> > +
> > +	TEST_ASSERT(vcpu, "Cannot find vcpu %u", vcpuid);
> > +
> > +	if (!vcpu->dirty_gfns) {
> > +		vcpu->dirty_gfns_count = size / sizeof(struct kvm_dirty_gfn);
> > +		vcpu->dirty_gfns = mmap(NULL, size, PROT_READ | PROT_WRITE,
> > +					MAP_SHARED, vcpu->fd, vm->page_size *
> > +					KVM_DIRTY_LOG_PAGE_OFFSET);
> 
> 
> It looks to me that we don't write to dirty_gfn.
> 
> So PROT_READ should be sufficient.

Yes.  Thanks,

-- 
Peter Xu