Xen-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: "Roger Pau Monné" <roger.pau@citrix.com>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Wei Liu <wl@xen.org>, Jan Beulich <jbeulich@suse.com>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [Xen-devel] [PATCH v2 3/4] x86/nvmx: split updating RVI from SVI in nvmx_update_apicv
Date: Thu, 26 Mar 2020 10:19:36 +0100
Message-ID: <20200326091936.GJ28601@Air-de-Roger> (raw)
In-Reply-To: <AADFC41AFE54684AB9EE6CBC0274A5D19D7EA780@SHSMSX104.ccr.corp.intel.com>

On Thu, Mar 26, 2020 at 03:13:56AM +0000, Tian, Kevin wrote:
> > From: Roger Pau Monne <roger.pau@citrix.com>
> > Sent: Wednesday, March 25, 2020 6:19 PM
> > 
> > Updating SVI is required when an interrupt has been injected using the
> > Ack on exit VMEXIT feature, so that the in service interrupt in the
> > GUEST_INTR_STATUS matches the vector that is signaled in
> > VM_EXIT_INTR_INFO.
> > 
> > Updating RVI however is not tied to the Ack on exit feature, as it
> > signals the next vector to be injected, and hence should always be
> > updated to the next pending vector, regardless of whether Ack on exit
> > is enabled.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > ---
> >  xen/arch/x86/hvm/vmx/vvmx.c | 22 +++++++++++++++++-----
> >  1 file changed, 17 insertions(+), 5 deletions(-)
> > 
> > diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
> > index 1753005c91..8431c912a1 100644
> > --- a/xen/arch/x86/hvm/vmx/vvmx.c
> > +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> > @@ -1384,26 +1384,38 @@ static void nvmx_update_apicv(struct vcpu *v)
> >      struct nestedvmx *nvmx = &vcpu_2_nvmx(v);
> >      unsigned long reason = get_vvmcs(v, VM_EXIT_REASON);
> >      unsigned long intr_info = get_vvmcs(v, VM_EXIT_INTR_INFO);
> > +    int rvi;
> > 
> >      if ( reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
> >           nvmx->intr.source == hvm_intsrc_lapic &&
> >           (intr_info & INTR_INFO_VALID_MASK) )
> >      {
> >          uint16_t status;
> > -        uint32_t rvi, ppr;
> > -        uint32_t vector = intr_info & 0xff;
> > +        uint32_t ppr;
> > +        unsigned int vector = intr_info & INTR_INFO_VECTOR_MASK;
> >          struct vlapic *vlapic = vcpu_vlapic(v);
> > 
> > +        /*
> > +         * Update SVI to record the currently in service interrupt that's
> > +         * signaled in EXIT_INTR_INFO.
> > +         */
> >          vlapic_ack_pending_irq(v, vector, 1);
> > 
> >          ppr = vlapic_set_ppr(vlapic);
> >          WARN_ON((ppr & 0xf0) != (vector & 0xf0));
> > 
> >          status = vector << VMX_GUEST_INTR_STATUS_SVI_OFFSET;
> > -        rvi = vlapic_has_pending_irq(v);
> > -        if ( rvi != -1 )
> > -            status |= rvi & VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
> > +        __vmwrite(GUEST_INTR_STATUS, status);
> > +    }
> > +
> > +    rvi = vlapic_has_pending_irq(v);
> > +    if ( rvi != -1 )
> > +    {
> > +        unsigned long status;
> > 
> > +        __vmread(GUEST_INTR_STATUS, &status);
> > +        status &= ~VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
> > +        status |= rvi & VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
> >          __vmwrite(GUEST_INTR_STATUS, status);
> >      }
> 
> I have two minor comments. First, original code requires only one
> __vmwrite but now needs two writes and one read for Ack-on-exit
> is set. Can we optimize to sustain the original behavior?

I think I can manage to do a single write by using a global status
variable initialized to 0 and only do the vmwrite if the value is != 0
by the end of the function.

> Second,
> although I didn't come up a case where always updating RVI (w/
> pending interrupt) may bring some bad effect, it is anyway safer
> to put the whole logic within the check of vmexit reason and intr 
> source.

I also considered this and decided there was no harm in always
updating RVI if there's a pending interrupt, it could even prevent a
future VMEXIT to update RVI AFAICT?

If you prefer I can return early from the function if reason !=
EXIT_REASON_EXTERNAL_INTERRUPT.

Thanks, Roger.


  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-25 10:19 [Xen-devel] [PATCH v2 0/4] x86/nvmx: fixes for interrupt injection Roger Pau Monne
2020-03-25 10:19 ` [Xen-devel] [PATCH v2 1/4] Revert "x86/vvmx: fix virtual interrupt injection when Ack on exit control is used" Roger Pau Monne
2020-03-25 10:19 ` [Xen-devel] [PATCH v2 2/4] x86/nvmx: only update SVI when using Ack on exit Roger Pau Monne
2020-03-26  2:48   ` Tian, Kevin
2020-03-25 10:19 ` [Xen-devel] [PATCH v2 3/4] x86/nvmx: split updating RVI from SVI in nvmx_update_apicv Roger Pau Monne
2020-03-26  3:13   ` Tian, Kevin
2020-03-26  9:19     ` Roger Pau Monné [this message]
2020-03-26  9:24       ` Tian, Kevin
2020-03-25 10:19 ` [Xen-devel] [PATCH v2 4/4] x86/nvmx: update exit bitmap when using virtual interrupt delivery Roger Pau Monne
2020-03-26  3:17   ` Tian, Kevin
2020-03-26  9:22     ` Roger Pau Monné
2020-03-26  9:26       ` Tian, Kevin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200326091936.GJ28601@Air-de-Roger \
    --to=roger.pau@citrix.com \
    --cc=andrew.cooper3@citrix.com \
    --cc=jbeulich@suse.com \
    --cc=jun.nakajima@intel.com \
    --cc=kevin.tian@intel.com \
    --cc=wl@xen.org \
    --cc=xen-devel@lists.xenproject.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Xen-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/xen-devel/0 xen-devel/git/0.git
	git clone --mirror https://lore.kernel.org/xen-devel/1 xen-devel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 xen-devel xen-devel/ https://lore.kernel.org/xen-devel \
		xen-devel@lists.xenproject.org xen-devel@lists.xen.org
	public-inbox-index xen-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.xenproject.lists.xen-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git