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Re: [Qemu-devel] [PATCH v3 2/2] intel-iommu: extend VTD emulation to all


From: Yu Zhang
Subject: Re: [Qemu-devel] [PATCH v3 2/2] intel-iommu: extend VTD emulation to allow 57-bit IOVA address width.
Date: Sat, 22 Dec 2018 00:19:20 +0800
User-agent: NeoMutt/20180622-66-b94505

On Thu, Dec 20, 2018 at 01:28:21PM -0500, Michael S. Tsirkin wrote:
> On Thu, Dec 20, 2018 at 01:49:21PM +0800, Yu Zhang wrote:
> > On Wed, Dec 19, 2018 at 10:23:44AM -0500, Michael S. Tsirkin wrote:
> > > On Wed, Dec 19, 2018 at 01:57:43PM +0800, Yu Zhang wrote:
> > > > On Tue, Dec 18, 2018 at 11:35:34PM -0500, Michael S. Tsirkin wrote:
> > > > > On Wed, Dec 19, 2018 at 11:40:06AM +0800, Yu Zhang wrote:
> > > > > > On Tue, Dec 18, 2018 at 09:49:02AM -0500, Michael S. Tsirkin wrote:
> > > > > > > On Tue, Dec 18, 2018 at 09:45:41PM +0800, Yu Zhang wrote:
> > > > > > > > On Tue, Dec 18, 2018 at 07:43:28AM -0500, Michael S. Tsirkin 
> > > > > > > > wrote:
> > > > > > > > > On Tue, Dec 18, 2018 at 06:01:16PM +0800, Yu Zhang wrote:
> > > > > > > > > > On Tue, Dec 18, 2018 at 05:47:14PM +0800, Yu Zhang wrote:
> > > > > > > > > > > On Mon, Dec 17, 2018 at 02:29:02PM +0100, Igor Mammedov 
> > > > > > > > > > > wrote:
> > > > > > > > > > > > On Wed, 12 Dec 2018 21:05:39 +0800
> > > > > > > > > > > > Yu Zhang <address@hidden> wrote:
> > > > > > > > > > > > 
> > > > > > > > > > > > > A 5-level paging capable VM may choose to use 57-bit 
> > > > > > > > > > > > > IOVA address width.
> > > > > > > > > > > > > E.g. guest applications may prefer to use its VA as 
> > > > > > > > > > > > > IOVA when performing
> > > > > > > > > > > > > VFIO map/unmap operations, to avoid the burden of 
> > > > > > > > > > > > > managing the IOVA space.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > This patch extends the current vIOMMU logic to cover 
> > > > > > > > > > > > > the extended address
> > > > > > > > > > > > > width. When creating a VM with 5-level paging 
> > > > > > > > > > > > > feature, one can choose to
> > > > > > > > > > > > > create a virtual VTD with 5-level paging capability, 
> > > > > > > > > > > > > with configurations
> > > > > > > > > > > > > like "-device intel-iommu,x-aw-bits=57".
> > > > > > > > > > > > > 
> > > > > > > > > > > > > Signed-off-by: Yu Zhang <address@hidden>
> > > > > > > > > > > > > Reviewed-by: Peter Xu <address@hidden>
> > > > > > > > > > > > > ---
> > > > > > > > > > > > > Cc: "Michael S. Tsirkin" <address@hidden>
> > > > > > > > > > > > > Cc: Marcel Apfelbaum <address@hidden>
> > > > > > > > > > > > > Cc: Paolo Bonzini <address@hidden>
> > > > > > > > > > > > > Cc: Richard Henderson <address@hidden>
> > > > > > > > > > > > > Cc: Eduardo Habkost <address@hidden>
> > > > > > > > > > > > > Cc: Peter Xu <address@hidden>
> > > > > > > > > > > > > ---
> > > > > > > > > > > > >  hw/i386/intel_iommu.c          | 53 
> > > > > > > > > > > > > ++++++++++++++++++++++++++++++++----------
> > > > > > > > > > > > >  hw/i386/intel_iommu_internal.h | 10 ++++++--
> > > > > > > > > > > > >  include/hw/i386/intel_iommu.h  |  1 +
> > > > > > > > > > > > >  3 files changed, 50 insertions(+), 14 deletions(-)
> > > > > > > > > > > > > 
> > > > > > > > > > > > > diff --git a/hw/i386/intel_iommu.c 
> > > > > > > > > > > > > b/hw/i386/intel_iommu.c
> > > > > > > > > > > > > index 0e88c63..871110c 100644
> > > > > > > > > > > > > --- a/hw/i386/intel_iommu.c
> > > > > > > > > > > > > +++ b/hw/i386/intel_iommu.c
> > > > > > > > > > > > > @@ -664,16 +664,16 @@ static inline bool 
> > > > > > > > > > > > > vtd_iova_range_check(uint64_t iova, VTDContextEntry 
> > > > > > > > > > > > > *ce,
> > > > > > > > > > > > >  
> > > > > > > > > > > > >  /*
> > > > > > > > > > > > >   * Rsvd field masks for spte:
> > > > > > > > > > > > > - *     Index [1] to [4] 4k pages
> > > > > > > > > > > > > - *     Index [5] to [8] large pages
> > > > > > > > > > > > > + *     Index [1] to [5] 4k pages
> > > > > > > > > > > > > + *     Index [6] to [10] large pages
> > > > > > > > > > > > >   */
> > > > > > > > > > > > > -static uint64_t vtd_paging_entry_rsvd_field[9];
> > > > > > > > > > > > > +static uint64_t vtd_paging_entry_rsvd_field[11];
> > > > > > > > > > > > >  
> > > > > > > > > > > > >  static bool vtd_slpte_nonzero_rsvd(uint64_t slpte, 
> > > > > > > > > > > > > uint32_t level)
> > > > > > > > > > > > >  {
> > > > > > > > > > > > >      if (slpte & VTD_SL_PT_PAGE_SIZE_MASK) {
> > > > > > > > > > > > >          /* Maybe large page */
> > > > > > > > > > > > > -        return slpte & 
> > > > > > > > > > > > > vtd_paging_entry_rsvd_field[level + 4];
> > > > > > > > > > > > > +        return slpte & 
> > > > > > > > > > > > > vtd_paging_entry_rsvd_field[level + 5];
> > > > > > > > > > > > >      } else {
> > > > > > > > > > > > >          return slpte & 
> > > > > > > > > > > > > vtd_paging_entry_rsvd_field[level];
> > > > > > > > > > > > >      }
> > > > > > > > > > > > > @@ -3127,6 +3127,8 @@ static void 
> > > > > > > > > > > > > vtd_init(IntelIOMMUState *s)
> > > > > > > > > > > > >               VTD_CAP_SAGAW_39bit | 
> > > > > > > > > > > > > VTD_CAP_MGAW(s->aw_bits);
> > > > > > > > > > > > >      if (s->aw_bits == VTD_AW_48BIT) {
> > > > > > > > > > > > >          s->cap |= VTD_CAP_SAGAW_48bit;
> > > > > > > > > > > > > +    } else if (s->aw_bits == VTD_AW_57BIT) {
> > > > > > > > > > > > > +        s->cap |= VTD_CAP_SAGAW_57bit | 
> > > > > > > > > > > > > VTD_CAP_SAGAW_48bit;
> > > > > > > > > > > > >      }
> > > > > > > > > > > > >      s->ecap = VTD_ECAP_QI | VTD_ECAP_IRO;
> > > > > > > > > > > > >      s->haw_bits = cpu->phys_bits;
> > > > > > > > > > > > > @@ -3139,10 +3141,12 @@ static void 
> > > > > > > > > > > > > vtd_init(IntelIOMMUState *s)
> > > > > > > > > > > > >      vtd_paging_entry_rsvd_field[2] = 
> > > > > > > > > > > > > VTD_SPTE_PAGE_L2_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > >      vtd_paging_entry_rsvd_field[3] = 
> > > > > > > > > > > > > VTD_SPTE_PAGE_L3_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > >      vtd_paging_entry_rsvd_field[4] = 
> > > > > > > > > > > > > VTD_SPTE_PAGE_L4_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > -    vtd_paging_entry_rsvd_field[5] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L1_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > -    vtd_paging_entry_rsvd_field[6] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L2_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > -    vtd_paging_entry_rsvd_field[7] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L3_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > -    vtd_paging_entry_rsvd_field[8] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L4_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > +    vtd_paging_entry_rsvd_field[5] = 
> > > > > > > > > > > > > VTD_SPTE_PAGE_L5_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > +    vtd_paging_entry_rsvd_field[6] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L1_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > +    vtd_paging_entry_rsvd_field[7] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L2_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > +    vtd_paging_entry_rsvd_field[8] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L3_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > +    vtd_paging_entry_rsvd_field[9] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L4_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > > +    vtd_paging_entry_rsvd_field[10] = 
> > > > > > > > > > > > > VTD_SPTE_LPAGE_L5_RSVD_MASK(s->haw_bits);
> > > > > > > > > > > > >  
> > > > > > > > > > > > >      if (x86_iommu->intr_supported) {
> > > > > > > > > > > > >          s->ecap |= VTD_ECAP_IR | VTD_ECAP_MHMV;
> > > > > > > > > > > > > @@ -3241,6 +3245,23 @@ static AddressSpace 
> > > > > > > > > > > > > *vtd_host_dma_iommu(PCIBus *bus, void *opaque, int 
> > > > > > > > > > > > > devfn)
> > > > > > > > > > > > >      return &vtd_as->as;
> > > > > > > > > > > > >  }
> > > > > > > > > > > > >  
> > > > > > > > > > > > > +static bool host_has_la57(void)
> > > > > > > > > > > > > +{
> > > > > > > > > > > > > +    uint32_t ecx, unused;
> > > > > > > > > > > > > +
> > > > > > > > > > > > > +    host_cpuid(7, 0, &unused, &unused, &ecx, 
> > > > > > > > > > > > > &unused);
> > > > > > > > > > > > > +    return ecx & CPUID_7_0_ECX_LA57;
> > > > > > > > > > > > > +}
> > > > > > > > > > > > > +
> > > > > > > > > > > > > +static bool guest_has_la57(void)
> > > > > > > > > > > > > +{
> > > > > > > > > > > > > +    CPUState *cs = first_cpu;
> > > > > > > > > > > > > +    X86CPU *cpu = X86_CPU(cs);
> > > > > > > > > > > > > +    CPUX86State *env = &cpu->env;
> > > > > > > > > > > > > +
> > > > > > > > > > > > > +    return env->features[FEAT_7_0_ECX] & 
> > > > > > > > > > > > > CPUID_7_0_ECX_LA57;
> > > > > > > > > > > > > +}
> > > > > > > > > > > > another direct access to CPU fields,
> > > > > > > > > > > > I'd suggest to set this value when iommu is created
> > > > > > > > > > > > i.e. add 'la57' property and set from iommu owner.
> > > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > Sorry, do you mean "-device intel-iommu,la57"? I think we 
> > > > > > > > > > > do not need
> > > > > > > > > > > that, because a 5-level capable vIOMMU can be created 
> > > > > > > > > > > with properties
> > > > > > > > > > > like "-device intel-iommu,x-aw-bits=57". 
> > > > > > > > > > > 
> > > > > > > > > > > The guest CPU fields are checked to make sure the VM has 
> > > > > > > > > > > LA57 CPU feature,
> > > > > > > > > > > because I believe there shall be no 5-level IOMMU on 
> > > > > > > > > > > platforms without LA57
> > > > > > > > > > > CPUs. 
> > > > > > > > > 
> > > > > > > > > I don't necessarily see why these need to be connected.
> > > > > > > > > If yes pls add code to explain.
> > > > > > > > 
> > > > > > > > Sorry, do you mean the VM shall be able to see a 5-level IOMMU 
> > > > > > > > even it does not
> > > > > > > > have LA57 feature? I do not see any direct connection when 
> > > > > > > > asked to enable a 5-level
> > > > > > > > vIOMMU at first, but I was told(and checked) that DPDK in the 
> > > > > > > > VM may choose a VA
> > > > > > > > value as an IOVA.
> > > > > > > 
> > > > > > > Right but then that doesn't work on all hosts either.
> > > > > > 
> > > > > > Oh, the host already has 5-level IOMMU now. So I think DPDK in 
> > > > > > native shall work with that.
> > > > > > 
> > > > > > > 
> > > > > > > > And if guest has LA57, we should create a 5-level vIOMMU to the 
> > > > > > > > VM.
> > > > > > > > But if the VM even does not have LA57, any specific reason we 
> > > > > > > > should give it a 5-level
> > > > > > > > vIOMMU?
> > > > > > > 
> > > > > > > So the example you give is VTD address width < CPU aw. That is 
> > > > > > > known
> > > > > > > to be problematic for dpdk but not for other software and maybe 
> > > > > > > dpdk
> > > > > > > will learns how to cope. Given such hosts exist it might be
> > > > > > > useful to support this at least for debugging.
> > > > > > > 
> > > > > > > Are there reasons to worry about VTD > CPU?
> > > > > > 
> > > > > > Well, I am not that worried(no usage case is one concern). I am OK 
> > > > > > to drop the guest check. :)
> > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > > > > >  static bool vtd_decide_config(IntelIOMMUState *s, 
> > > > > > > > > > > > > Error **errp)
> > > > > > > > > > > > >  {
> > > > > > > > > > > > >      X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(s);
> > > > > > > > > > > > > @@ -3267,11 +3288,19 @@ static bool 
> > > > > > > > > > > > > vtd_decide_config(IntelIOMMUState *s, Error **errp)
> > > > > > > > > > > > >          }
> > > > > > > > > > > > >      }
> > > > > > > > > > > > >  
> > > > > > > > > > > > > -    /* Currently only address widths supported are 
> > > > > > > > > > > > > 39 and 48 bits */
> > > > > > > > > > > > > +    /* Currently address widths supported are 39, 
> > > > > > > > > > > > > 48, and 57 bits */
> > > > > > > > > > > > >      if ((s->aw_bits != VTD_AW_39BIT) &&
> > > > > > > > > > > > > -        (s->aw_bits != VTD_AW_48BIT)) {
> > > > > > > > > > > > > -        error_setg(errp, "Supported values for 
> > > > > > > > > > > > > x-aw-bits are: %d, %d",
> > > > > > > > > > > > > -                   VTD_AW_39BIT, VTD_AW_48BIT);
> > > > > > > > > > > > > +        (s->aw_bits != VTD_AW_48BIT) &&
> > > > > > > > > > > > > +        (s->aw_bits != VTD_AW_57BIT)) {
> > > > > > > > > > > > > +        error_setg(errp, "Supported values for 
> > > > > > > > > > > > > x-aw-bits are: %d, %d, %d",
> > > > > > > > > > > > > +                   VTD_AW_39BIT, VTD_AW_48BIT, 
> > > > > > > > > > > > > VTD_AW_57BIT);
> > > > > > > > > > > > > +        return false;
> > > > > > > > > > > > > +    }
> > > > > > > > > > > > > +
> > > > > > > > > > > > > +    if ((s->aw_bits == VTD_AW_57BIT) &&
> > > > > > > > > > > > > +        !(host_has_la57() && guest_has_la57())) {
> > > > > > > > > > > > Does iommu supposed to work in TCG mode?
> > > > > > > > > > > > If yes then why it should care about host_has_la57()?
> > > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > Hmm... I did not take TCG mode into consideration. And 
> > > > > > > > > > > host_has_la57() is
> > > > > > > > > > > used to guarantee the host have la57 feature so that 
> > > > > > > > > > > iommu shadowing works
> > > > > > > > > > > for device assignment.
> > > > > > > > > > > 
> > > > > > > > > > > I guess iommu shall work in TCG mode(though I am not 
> > > > > > > > > > > quite sure about this).
> > > > > > > > > > > But I do not have any usage case of a 5-level vIOMMU in 
> > > > > > > > > > > TCG in mind. So maybe
> > > > > > > > > > > we can:
> > > > > > > > > > > 1> check the 'ms->accel' in vtd_decide_config() and do 
> > > > > > > > > > > not care about host
> > > > > > > > > > > capability if it is TCG.
> > > > > > > > > > 
> > > > > > > > > > For choice 1, kvm_enabled() might be used instead of 
> > > > > > > > > > ms->accel. Thanks Peter
> > > > > > > > > > for the remind. :)
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > This needs a big comment with an explanation though.
> > > > > > > > > And probably a TODO to make it work under TCG ...
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > Thanks, Michael. For choice 1, I believe it should work for 
> > > > > > > > TCG(will need test
> > > > > > > > though), and the condition would be sth. like:
> > > > > > > > 
> > > > > > > >     if ((s->aw_bits == VTD_AW_57BIT) &&
> > > > > > > >         kvm_enabled() &&
> > > > > > > >         !host_has_la57())  {
> > > > > > > > 
> > > > > > > > As you can see, though I remove the check of guest_has_la57(), 
> > > > > > > > I still kept the
> > > > > > > > check against host when KVM is enabled. I'm still ready to be 
> > > > > > > > convinced for any
> > > > > > > > requirement why we do not need the guest check. :) 
> > > > > > > 
> > > > > > > 
> > > > > > > okay but then (repeating myself, sorry) pls add a comment that 
> > > > > > > explains
> > > > > > > what happens if you do not add this limitation.
> > > > > > 
> > > > > > How about below comments?
> > > > > >     /*
> > > > > >      * For KVM guests, the host capability of LA57 shall be 
> > > > > > available,
> > > > > 
> > > > > So why is host CPU LA57 necessary for shadowing? Could you explain 
> > > > > pls?
> > > > 
> > > > Oh, let me try to explain the background here. :)
> > > > 
> > > > Currently, vIOMMU in qemu does not have logic to check against the 
> > > > hardware
> > > > IOMMU capability. E.g. when we create an IOMMU with 48 bit DMA address 
> > > > width,
> > > > qemu does not check if any physical IOMMU has such support. And the 
> > > > shadow
> > > > IOMMU logic will have problem if host IOMMU only supports 39 bit IOVA. 
> > > > And
> > > > we will have the same problem when it comes to 57 bit IOVA.
> > > > 
> > > > My previous discussion with Peter Xu reached an agreement that for now, 
> > > > we
> > > > just use the host cpu capability as a reference when trying to create a 
> > > > 5-level
> > > > vIOMMU, because 57 bit IOMMU hardware will not come until ICX 
> > > > platform(which
> > > > includes LA57). 
> > > > 
> > > > And the final correct solution should be to enumerate the capabilities 
> > > > of
> > > > hardware IOMMUs used by the assigned device, and reject if any dismatch 
> > > > is
> > > > found.
> > > 
> > > Right. And it's a hack because
> > > 1. CPU AW doesn't always match VTD AW
> > > 2. The limitation only applies to hardware devices, software ones are fine
> > > So we need a patch for the host sysfs to expose the actual IOMMU AW to 
> > > userspace.
> > > QEMU could then look at the actual hardware features.
> > > I'd like to see the actual patch doing that, even if we
> > > add a hack based on CPU AW for existing systems.
> > > 
> > 
> > Sure, I have plan to do so. And I am wondering, if this is a must for 
> > current
> > patchset to be accepted? I mean, after all, we already have the same problem
> > on existing platform. :)
> 
> I'd like to avoid poking at the CPU from VTD code. That's all.

OK. So for the short term´╝îhow about I remove the check of host cpu, and add a 
TODO
in the comments in vtd_decide_config()? 

As to the check against hardware IOMMU, Peter once had a proposal in
http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg02281.html

Do you have any comment or suggestion on Peter's proposal? I still do not quite 
know
how to do it for now...

[...]


B.R.
Yu



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