From: Adrian Pop <apop@bitdefender.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Tamas K Lengyel <tamas@tklengyel.com>,
Wei Liu <wei.liu2@citrix.com>,
Razvan Cojocaru <rcojocaru@bitdefender.com>,
George Dunlap <george.dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH 2/3] x86/altp2m: Add a hvmop for setting the suppress #VE bit
Date: Tue, 6 Jun 2017 16:00:59 +0300 [thread overview]
Message-ID: <20170606130059.GA12361@hel> (raw)
In-Reply-To: <592C4E89020000780015D524@prv-mh.provo.novell.com>
Hello,
On Mon, May 29, 2017 at 08:38:33AM -0600, Jan Beulich wrote:
> >>> On 18.05.17 at 17:07, <apop@bitdefender.com> wrote:
> > --- a/xen/arch/x86/mm/mem_access.c
> > +++ b/xen/arch/x86/mm/mem_access.c
> > @@ -466,6 +466,54 @@ int p2m_get_mem_access(struct domain *d, gfn_t gfn, xenmem_access_t *access)
> > }
> >
> > /*
> > + * Set/clear the #VE suppress bit for a page. Only available on VMX.
> > + */
> > +int p2m_set_suppress_ve(struct domain *d, gfn_t gfn, uint8_t suppress_ve,
>
> suppress_ve presumably is meant to be boolean.
Yes. It can be changed to bool.
> > + unsigned int altp2m_idx)
> > +{
> > + struct p2m_domain *host_p2m = p2m_get_hostp2m(d);
> > + struct p2m_domain *ap2m = NULL;
> > + struct p2m_domain *p2m = NULL;
>
> Pointless initializer.
Ok.
> > + mfn_t mfn;
> > + p2m_access_t a;
> > + p2m_type_t t;
> > + unsigned long gfn_l;
>
> Please avoid this local variable and use gfn_x() in the two places
> you need to.
Sure.
> > + int rc = 0;
>
> Pointless initializer again.
Right.
> > +
> > + if ( !cpu_has_vmx )
> > + return -EOPNOTSUPP;
>
> Is this enough? Wouldn't it be better to signal the caller whenever
> hardware (or even software) isn't going to honor the request?
Well, the caller checks the return value. The libxc function
xc_altp2m_set_suppress_ve for instance will return a negative in this
case.
> > + if ( altp2m_idx > 0 )
> > + {
> > + if ( altp2m_idx >= MAX_ALTP2M ||
> > + d->arch.altp2m_eptp[altp2m_idx] == mfn_x(INVALID_MFN) )
>
> Indentation.
Ok.
> > + return -EINVAL;
> > +
> > + p2m = ap2m = d->arch.altp2m_p2m[altp2m_idx];
> > + }
> > + else
> > + {
> > + p2m = host_p2m;
> > + }
>
> Unnecessary braces.
Ok.
> > + p2m_lock(host_p2m);
> > + if ( ap2m )
> > + p2m_lock(ap2m);
> > +
> > + gfn_l = gfn_x(gfn);
> > + mfn = p2m->get_entry(p2m, gfn_l, &t, &a, 0, NULL, NULL);
> > + if ( !mfn_valid(mfn) )
> > + return -ESRCH;
> > + rc = p2m->set_entry(p2m, gfn_l, mfn, PAGE_ORDER_4K, t, a,
> > + suppress_ve);
> > + if ( ap2m )
> > + p2m_unlock(ap2m);
> > + p2m_unlock(host_p2m);
>
> To fiddle with a single gfn, this looks to be very heavy locking.
> While for now gfn_lock() is the same as p2m_lock(), from an
> abstract perspective I'd expect gfn_lock() to suffice here at
> least in the non-altp2m case.
Ok.
> And then there are two general questions: Without a libxc layer
> function, how is one supposed to use this new sub-op? Is it
> really intended to permit a guest to call this for itself?
Well, the sub-op could be used from a Linux kernel module if libxc is
not available if struct xen_hvm_altp2m_op and struct
xen_hvm_altp2m_set_suppress_ve are defined.
Our use case, though, involves either Dom0 or a "privileged" DomU
altering the suppress #VE bit for the target guest.
> Jan
>
Thanks!
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next prev parent reply other threads:[~2017-06-06 13:01 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-18 15:07 [PATCH 0/3] x86: Add a hvmop for setting the #VE suppress bit Adrian Pop
2017-05-18 15:07 ` [PATCH 1/3] x86/mm: Change default value for suppress #VE in set_mem_access() Adrian Pop
2017-05-18 15:07 ` [PATCH 2/3] x86/altp2m: Add a hvmop for setting the suppress #VE bit Adrian Pop
2017-05-18 17:27 ` Tamas K Lengyel
2017-05-23 12:03 ` Adrian Pop
2017-05-29 14:38 ` Jan Beulich
2017-06-06 13:00 ` Adrian Pop [this message]
2017-06-06 13:08 ` Jan Beulich
2017-06-08 13:49 ` Adrian Pop
2017-06-08 14:08 ` Jan Beulich
2017-06-09 14:18 ` Adrian Pop
2017-05-18 15:07 ` [PATCH 3/3] libxc: Add support for the altp2m suppress #VE hvmop Adrian Pop
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