linux-kernel - Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

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Date:   Mon, 19 Dec 2022 16:15:32 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

On Fri, Dec 16, 2022 at 04:09:06PM +0100, Borislav Petkov wrote:
> On Fri, Dec 02, 2022 at 02:13:40PM +0800, Chao Peng wrote:
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 1782c4555d94..7f0f5e9f2406 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> >  	spin_lock_init(&kvm->mn_invalidate_lock);
> >  	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
> >  	xa_init(&kvm->vcpu_array);
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +	xa_init(&kvm->mem_attr_array);
> > +#endif
> 
> 	if (IS_ENABLED(CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES))
> 		...
> 
> would at least remove the ugly ifdeffery.
> 
> Or you could create wrapper functions for that xa_init() and
> xa_destroy() and put the ifdeffery in there.

Agreed.

> 
> > @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
> >  }
> >  #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
> >  
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> 
> I guess that function should have a verb in the name:
> 
> kvm_get_supported_mem_attributes()

Right!
> 
> > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > +					   struct kvm_memory_attributes *attrs)
> > +{
> > +	gfn_t start, end;
> > +	unsigned long i;
> > +	void *entry;
> > +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +	/* flags is currently not used. */
> > +	if (attrs->flags)
> > +		return -EINVAL;
> > +	if (attrs->attributes & ~supported_attrs)
> > +		return -EINVAL;
> > +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > +		return -EINVAL;
> > +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > +		return -EINVAL;
> 
> Dunno, shouldn't those issue some sort of an error message so that the
> caller knows where it failed? Or at least return different retvals which
> signal what the problem is?

Tamping down with error number a bit:

        if (attrs->flags)
                return -ENXIO;
        if (attrs->attributes & ~supported_attrs)
                return -EOPNOTSUPP;
        if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size) ||
            attrs->size == 0)
                return -EINVAL;
        if (attrs->address + attrs->size < attrs->address)
                return -E2BIG;

Chao
> 
> > +	start = attrs->address >> PAGE_SHIFT;
> > +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> > +
> > +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > +
> > +	mutex_lock(&kvm->lock);
> > +	for (i = start; i < end; i++)
> > +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > +				    GFP_KERNEL_ACCOUNT)))
> > +			break;
> > +	mutex_unlock(&kvm->lock);
> > +
> > +	attrs->address = i << PAGE_SHIFT;
> > +	attrs->size = (end - i) << PAGE_SHIFT;
> > +
> > +	return 0;
> > +}
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette