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d="scan'208";a="14999728" Date: Thu, 26 Mar 2020 10:19:36 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: "Tian, Kevin" Message-ID: <20200326091936.GJ28601@Air-de-Roger> References: <20200325101910.29168-1-roger.pau@citrix.com> <20200325101910.29168-4-roger.pau@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: AMSPEX02CAS01.citrite.net (10.69.22.112) To AMSPEX02CL02.citrite.net (10.69.22.126) Subject: Re: [Xen-devel] [PATCH v2 3/4] x86/nvmx: split updating RVI from SVI in nvmx_update_apicv X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: "xen-devel@lists.xenproject.org" , Wei Liu , Jan Beulich , "Nakajima, Jun" , Andrew Cooper Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On Thu, Mar 26, 2020 at 03:13:56AM +0000, Tian, Kevin wrote: > > From: Roger Pau Monne > > 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 > > --- > > 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.