| Message ID | 20200731142604.30149-2-paul@xen.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | epte_get_entry_emt() modifications | expand |
> -----Original Message----- > From: Paul Durrant <paul@xen.org> > Sent: 31 July 2020 15:26 > To: xen-devel@lists.xenproject.org > Cc: Durrant, Paul <pdurrant@amazon.co.uk>; Jan Beulich <jbeulich@suse.com>; Andrew Cooper > <andrew.cooper3@citrix.com>; Wei Liu <wl@xen.org>; Roger Pau Monné <roger.pau@citrix.com> > Subject: [EXTERNAL] [PATCH v3 1/2] x86/hvm: set 'ipat' in EPT for special pages > > CAUTION: This email originated from outside of the organization. Do not click links or open > attachments unless you can confirm the sender and know the content is safe. > > > > From: Paul Durrant <pdurrant@amazon.com> > > All non-MMIO ranges (i.e those not mapping real device MMIO regions) that > map valid MFNs are normally marked MTRR_TYPE_WRBACK and 'ipat' is set. Hence > when PV drivers running in a guest populate the BAR space of the Xen Platform > PCI Device with pages such as the Shared Info page or Grant Table pages, > accesses to these pages will be cachable. > > However, should IOMMU mappings be enabled be enabled for the guest then these > accesses become uncachable. This has a substantial negative effect on I/O > throughput of PV devices. Arguably PV drivers should bot be using BAR space to > host the Shared Info and Grant Table pages but it is currently commonplace for > them to do this and so this problem needs mitigation. Hence this patch makes > sure the 'ipat' bit is set for any special page regardless of where in GFN > space it is mapped. > > NOTE: Clearly this mitigation only applies to Intel EPT. It is not obvious > that there is any similar mitigation possible for AMD NPT. Downstreams > such as Citrix XenServer have been carrying a patch similar to this for > several releases though. > > Signed-off-by: Paul Durrant <pdurrant@amazon.com> This is missing a hunk. I'll send v4. Paul > --- > Cc: Jan Beulich <jbeulich@suse.com> > Cc: Andrew Cooper <andrew.cooper3@citrix.com> > Cc: Wei Liu <wl@xen.org> > Cc: "Roger Pau Monné" <roger.pau@citrix.com> > > v3: > - dropping Jan's R-b > - cope with order > 0 > --- > xen/arch/x86/hvm/mtrr.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/xen/arch/x86/hvm/mtrr.c b/xen/arch/x86/hvm/mtrr.c > index 511c3be1c8..26721f6ee7 100644 > --- a/xen/arch/x86/hvm/mtrr.c > +++ b/xen/arch/x86/hvm/mtrr.c > @@ -836,6 +836,17 @@ int epte_get_entry_emt(struct domain *d, unsigned long gfn, mfn_t mfn, > return MTRR_TYPE_WRBACK; > } > > + for ( i = 0; i < (1ul << order); i++ ) > + { > + if ( is_special_page(mfn_to_page(mfn_add(mfn, i))) ) > + { > + if ( order ) > + return -1; > + *ipat = 1; > + return MTRR_TYPE_WRBACK; > + } > + } > + > gmtrr_mtype = hvm_get_mem_pinned_cacheattr(d, _gfn(gfn), order); > if ( gmtrr_mtype >= 0 ) > { > -- > 2.20.1
diff --git a/xen/arch/x86/hvm/mtrr.c b/xen/arch/x86/hvm/mtrr.c index 511c3be1c8..26721f6ee7 100644 --- a/xen/arch/x86/hvm/mtrr.c +++ b/xen/arch/x86/hvm/mtrr.c @@ -836,6 +836,17 @@ int epte_get_entry_emt(struct domain *d, unsigned long gfn, mfn_t mfn, return MTRR_TYPE_WRBACK; } + for ( i = 0; i < (1ul << order); i++ ) + { + if ( is_special_page(mfn_to_page(mfn_add(mfn, i))) ) + { + if ( order ) + return -1; + *ipat = 1; + return MTRR_TYPE_WRBACK; + } + } + gmtrr_mtype = hvm_get_mem_pinned_cacheattr(d, _gfn(gfn), order); if ( gmtrr_mtype >= 0 ) {