Re: [Qemu-devel] [PATCH v3 1/2] intel-iommu: differentiate host address width from IOVA address width.

[Michael S. Tsirkin]

On Tue, Dec 18, 2018 at 05:27:23PM +0800, Yu Zhang wrote:
> On Mon, Dec 17, 2018 at 02:17:40PM +0100, Igor Mammedov wrote:
> > On Wed, 12 Dec 2018 21:05:38 +0800
> > Yu Zhang <address@hidden> wrote:
> > 
> > > Currently, vIOMMU is using the value of IOVA address width, instead of
> > > the host address width(HAW) to calculate the number of reserved bits in
> > > data structures such as root entries, context entries, and entries of
> > > DMA paging structures etc.
> > > 
> > > However values of IOVA address width and of the HAW may not equal. For
> > > example, a 48-bit IOVA can only be mapped to host addresses no wider than
> > > 46 bits. Using 48, instead of 46 to calculate the reserved bit may result
> > > in an invalid IOVA being accepted.
> > > 
> > > To fix this, a new field - haw_bits is introduced in struct 
> > > IntelIOMMUState,
> > > whose value is initialized based on the maximum physical address set to
> > > guest CPU.
> > 
> > > Also, definitions such as VTD_HOST_AW_39/48BIT etc. are renamed
> > > to clarify.
> > > 
> > > Signed-off-by: Yu Zhang <address@hidden>
> > > Reviewed-by: Peter Xu <address@hidden>
> > > ---
> > [...]
> > 
> > > @@ -3100,6 +3104,8 @@ static void vtd_iommu_replay(IOMMUMemoryRegion 
> > > *iommu_mr, IOMMUNotifier *n)
> > >  static void vtd_init(IntelIOMMUState *s)
> > >  {
> > >      X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(s);
> > > +    CPUState *cs = first_cpu;
> > > +    X86CPU *cpu = X86_CPU(cs);
> > >  
> > >      memset(s->csr, 0, DMAR_REG_SIZE);
> > >      memset(s->wmask, 0, DMAR_REG_SIZE);
> > > @@ -3119,23 +3125,24 @@ static void vtd_init(IntelIOMMUState *s)
> > >      s->cap = VTD_CAP_FRO | VTD_CAP_NFR | VTD_CAP_ND |
> > >               VTD_CAP_MAMV | VTD_CAP_PSI | VTD_CAP_SLLPS |
> > >               VTD_CAP_SAGAW_39bit | VTD_CAP_MGAW(s->aw_bits);
> > > -    if (s->aw_bits == VTD_HOST_AW_48BIT) {
> > > +    if (s->aw_bits == VTD_AW_48BIT) {
> > >          s->cap |= VTD_CAP_SAGAW_48bit;
> > >      }
> > >      s->ecap = VTD_ECAP_QI | VTD_ECAP_IRO;
> > > +    s->haw_bits = cpu->phys_bits;
> > Is it possible to avoid accessing CPU fields directly or cpu altogether
> > and set phys_bits when iommu is created?
> 
> Thanks for your comments, Igor.
> 
> Well, I guess you prefer not to query the CPU capabilities while deciding
> the vIOMMU features. But to me, they are not that irrelevant.:)
> 
> Here the hardware address width in vt-d, and the one in cpuid.MAXPHYSADDR
> are referring to the same concept. In VM, both are the maximum guest physical
> address width. If we do not check the CPU field here, we will still have to
> check the CPU field in other places such as build_dmar_q35(), and reset the
> s->haw_bits again.
> 
> Is this explanation convincing enough? :)

So what happens if these don't match? I guess guest can configure the vtd
to put data into some memory which isn't then accessible to
the cpu, or cpu can use some memory not accessible to devices.

I guess some guests might be confused - is this what you
observe? If yes some comments that tell people which
guests get confused would be nice. Is windows happy? Is linux happy?



> > 
> > Perhaps Eduardo
> >  can suggest better approach, since he's more familiar with phys_bits topic
> 
> @Eduardo, any comments? Thanks!
> 
> > 
> > >      /*
> > >       * Rsvd field masks for spte
> > >       */
> > >      vtd_paging_entry_rsvd_field[0] = ~0ULL;
> > > -    vtd_paging_entry_rsvd_field[1] = 
> > > VTD_SPTE_PAGE_L1_RSVD_MASK(s->aw_bits);
> > > -    vtd_paging_entry_rsvd_field[2] = 
> > > VTD_SPTE_PAGE_L2_RSVD_MASK(s->aw_bits);
> > > -    vtd_paging_entry_rsvd_field[3] = 
> > > VTD_SPTE_PAGE_L3_RSVD_MASK(s->aw_bits);
> > > -    vtd_paging_entry_rsvd_field[4] = 
> > > VTD_SPTE_PAGE_L4_RSVD_MASK(s->aw_bits);
> > > -    vtd_paging_entry_rsvd_field[5] = 
> > > VTD_SPTE_LPAGE_L1_RSVD_MASK(s->aw_bits);
> > > -    vtd_paging_entry_rsvd_field[6] = 
> > > VTD_SPTE_LPAGE_L2_RSVD_MASK(s->aw_bits);
> > > -    vtd_paging_entry_rsvd_field[7] = 
> > > VTD_SPTE_LPAGE_L3_RSVD_MASK(s->aw_bits);
> > > -    vtd_paging_entry_rsvd_field[8] = 
> > > VTD_SPTE_LPAGE_L4_RSVD_MASK(s->aw_bits);
> > > +    vtd_paging_entry_rsvd_field[1] = 
> > > VTD_SPTE_PAGE_L1_RSVD_MASK(s->haw_bits);
> > > +    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);
> > >  
> > >      if (x86_iommu->intr_supported) {
> > >          s->ecap |= VTD_ECAP_IR | VTD_ECAP_MHMV;
> > > @@ -3261,10 +3268,10 @@ static bool vtd_decide_config(IntelIOMMUState *s, 
> > > Error **errp)
> > >      }
> > >  
> > >      /* Currently only address widths supported are 39 and 48 bits */
> > > -    if ((s->aw_bits != VTD_HOST_AW_39BIT) &&
> > > -        (s->aw_bits != VTD_HOST_AW_48BIT)) {
> > > +    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_HOST_AW_39BIT, VTD_HOST_AW_48BIT);
> > > +                   VTD_AW_39BIT, VTD_AW_48BIT);
> > >          return false;
> > >      }
> > >  
> > > diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
> > > index ed4e758..820451c 100644
> > > --- a/include/hw/i386/intel_iommu.h
> > > +++ b/include/hw/i386/intel_iommu.h
> > > @@ -47,9 +47,9 @@
> > >  #define VTD_SID_TO_DEVFN(sid)       ((sid) & 0xff)
> > >  
> > >  #define DMAR_REG_SIZE               0x230
> > > -#define VTD_HOST_AW_39BIT           39
> > > -#define VTD_HOST_AW_48BIT           48
> > > -#define VTD_HOST_ADDRESS_WIDTH      VTD_HOST_AW_39BIT
> > > +#define VTD_AW_39BIT                39
> > > +#define VTD_AW_48BIT                48
> > > +#define VTD_ADDRESS_WIDTH           VTD_AW_39BIT
> > >  #define VTD_HAW_MASK(aw)            ((1ULL << (aw)) - 1)
> > >  
> > >  #define DMAR_REPORT_F_INTR          (1)
> > > @@ -244,7 +244,8 @@ struct IntelIOMMUState {
> > >      bool intr_eime;                 /* Extended interrupt mode enabled */
> > >      OnOffAuto intr_eim;             /* Toggle for EIM cabability */
> > >      bool buggy_eim;                 /* Force buggy EIM unless eim=off */
> > > -    uint8_t aw_bits;                /* Host/IOVA address width (in bits) 
> > > */
> > > +    uint8_t aw_bits;                /* IOVA address width (in bits) */
> > > +    uint8_t haw_bits;               /* Hardware address width (in bits) 
> > > */
> > >  
> > >      /*
> > >       * Protects IOMMU states in general.  Currently it protects the
> > 
> > 
> 
> B.R.
> Yu