On Tue, 2 Jun 2026 16:18:06 -0700 Davidlohr Bueso <[email protected]> wrote:
> Expose the CFMWS Window Restrictions as named per-capability machine > properties (device-coherent, host-only, volatile, persistent, > fixed-config, back-invalidate), making the advertised restrictions > configurable per window. > > Signed-off-by: Davidlohr Bueso <[email protected]> Hi Davidlohr, looks good in general. Maybe I need more coffee but I don't thing the documented constraints are exactly the same as the ones in the code. Thanks again for doing this! Jonathan > --- > docs/system/devices/cxl.rst | 13 +++------ > hw/acpi/cxl.c | 2 +- > hw/cxl/cxl-host.c | 55 +++++++++++++++++++++++++++++++++++++ > include/hw/cxl/cxl.h | 12 ++++++++ > qapi/machine.json | 29 +++++++++++++++++++ > 5 files changed, 101 insertions(+), 10 deletions(-) > > diff --git a/docs/system/devices/cxl.rst b/docs/system/devices/cxl.rst > index 9d0771cdfd73..cf3f2c81785c 100644 > --- a/docs/system/devices/cxl.rst > +++ b/docs/system/devices/cxl.rst > @@ -384,15 +384,14 @@ An example of 4 devices below a switch suitable for 1, > 2 or 4 way interleave:: > -device > cxl-type3,bus=swport3,persistent-memdev=cxl-mem3,lsa=cxl-lsa3,id=cxl-pmem3,sn=0x4 > \ > -M > cxl-fmw.0.targets.0=cxl.1,cxl-fmw.0.size=4G,cxl-fmw.0.interleave-granularity=4k > > -An example of 4 type3 devices with volatile memory below a switch. Two of > the devices > -use HDM-DB for coherence, which requires operating in Flit mode:: > +An example of 2 type3 devices with volatile memory below a switch. The > devices > +use HDM-DB for coherence, which requires operating in Flit mode and a CXL > window > +configured to permit device-coherent Back-Invalidate model:: Thanks for doing this!. I wonder if the example should gain a second FMW to accommodate the original mixed device config. I'm fairly sure that should work and good to indicate that the mixed case is real. > > qemu-system-x86_64 -M q35,cxl=on -m 4G,maxmem=8G,slots=8 -smp 4 \ > ... > -object memory-backend-ram,id=cxl-mem0,share=on,size=256M \ > -object memory-backend-ram,id=cxl-mem1,share=on,size=256M \ > - -object memory-backend-ram,id=cxl-mem2,share=on,size=256M \ > - -object memory-backend-ram,id=cxl-mem3,share=on,size=256M \ > -device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.1 \ > -device cxl-rp,port=0,bus=cxl.1,id=root_port0,chassis=0,slot=0 \ > -device cxl-rp,port=1,bus=cxl.1,id=root_port1,chassis=0,slot=1 \ > @@ -401,11 +400,7 @@ use HDM-DB for coherence, which requires operating in > Flit mode:: > -device > cxl-type3,bus=swport0,volatile-memdev=cxl-mem0,id=cxl-mem0,sn=0x1,x-256b-flit=on,hdm-db=on > \ > -device cxl-downstream,port=1,bus=us0,id=swport1,chassis=0,slot=5 \ > -device > cxl-type3,bus=swport1,volatile-memdev=cxl-mem1,id=cxl-mem1,sn=0x2,x-256b-flit=on,hdm-db=on > \ > - -device cxl-downstream,port=2,bus=us0,id=swport2,chassis=0,slot=6 \ > - -device cxl-type3,bus=swport2,volatile-memdev=cxl-mem2,id=cxl-mem2,sn=0x3 \ > - -device cxl-downstream,port=3,bus=us0,id=swport3,chassis=0,slot=7 \ > - -device cxl-type3,bus=swport3,volatile-memdev=cxl-mem3,id=cxl-mem3,sn=0x4 \ > - -M > cxl-fmw.0.targets.0=cxl.1,cxl-fmw.0.size=4G,cxl-fmw.0.interleave-granularity=4k > + -M > cxl-fmw.0.targets.0=cxl.1,cxl-fmw.0.size=4G,cxl-fmw.0.interleave-granularity=4k,cxl-fmw.0.back-invalidate=on > > A simple arm/virt example featuring a single direct connected CXL Type 3 > Volatile Memory device:: > diff --git a/hw/acpi/cxl.c b/hw/acpi/cxl.c > index 5ce5e8e083ba..77c1db6561b4 100644 > --- a/hw/acpi/cxl.c > +++ b/hw/acpi/cxl.c > @@ -172,7 +172,7 @@ static void cedt_build_cfmws(CXLFixedWindow *fw, Aml > *cedt) > build_append_int_noprefix(table_data, fw->enc_int_gran, 4); > > /* Window Restrictions */ > - build_append_int_noprefix(table_data, 0xe, 2); > + build_append_int_noprefix(table_data, fw->restrictions, 2); > > /* QTG ID */ > build_append_int_noprefix(table_data, 0, 2); > diff --git a/hw/cxl/cxl-host.c b/hw/cxl/cxl-host.c > index f3479b19914f..7af431bf1555 100644 > --- a/hw/cxl/cxl-host.c > +++ b/hw/cxl/cxl-host.c > @@ -61,6 +61,61 @@ static void > cxl_fixed_memory_window_config(CXLFixedMemoryWindowOptions *object, > fw->enc_int_gran = 0; > } > > + if (object->device_coherent) { > + fw->restrictions |= CXL_FMW_DEVICE_COHERENT; > + } > + if (object->back_invalidate) { > + if (object->has_device_coherent && !object->device_coherent) { > + error_setg(errp, "CFMW BI requires device-coherent"); > + return; > + } > + fw->restrictions |= CXL_FMW_DEVICE_COHERENT | CXL_FMW_BI; > + } > + if (object->host_only) { > + fw->restrictions |= CXL_FMW_HOST_ONLY; > + } else if (!object->has_host_only && > + !(fw->restrictions & CXL_FMW_DEVICE_COHERENT)) { > + /* host-only coherent is the default when no model is requested. */ > + fw->restrictions |= CXL_FMW_HOST_ONLY; > + } > + > + if (!(fw->restrictions & (CXL_FMW_DEVICE_COHERENT | CXL_FMW_HOST_ONLY))) > { > + error_setg(errp, "CFMW coherency model required"); > + return; > + } > + > + /* > + * Reject the undefined and conflicting coherency combinations, > + * per CXL r4.0 9.18.1.3. > + */ > + if ((fw->restrictions & CXL_FMW_HOST_ONLY) && > + (fw->restrictions & CXL_FMW_BI)) { > + error_setg(errp, "CFMW host-only coherency + BI is undefined > behavior"); > + return; > + } > + if ((fw->restrictions & CXL_FMW_DEVICE_COHERENT) && > + (fw->restrictions & CXL_FMW_HOST_ONLY)) { > + error_setg(errp, > + "CFMW device and host-only coherency are mutually > exclusive"); I'm confused. I thought this one was allowed by the spec? Without a spec clarification I'm reluctant to prevent it. > + return; > + } > + > + if (object->fixed_config) { > + fw->restrictions |= CXL_FMW_FIXED_CONFIG; /* no-op */ > + } > + > + /* Volatile and persistent are permitted unless explicitly disabled. */ > + if (!object->has_q_volatile || object->q_volatile) { > + fw->restrictions |= CXL_FMW_VOLATILE; > + } > + if (!object->has_persistent || object->persistent) { > + fw->restrictions |= CXL_FMW_PERSISTENT; > + } > + if (!(fw->restrictions & (CXL_FMW_VOLATILE | CXL_FMW_PERSISTENT))) { > + error_setg(errp, "CFMW volatile and/or persistent memory required"); > + return; > + } > + > fw->targets = g_malloc0_n(fw->num_targets, sizeof(*fw->targets)); > for (i = 0, target = object->targets; target; i++, target = > target->next) { > /* This link cannot be resolved yet, so stash the name for now */ > diff --git a/qapi/machine.json b/qapi/machine.json > index 685e4e29b87d..a5be531403a1 100644 > --- a/qapi/machine.json > +++ b/qapi/machine.json > @@ -551,15 +551,44 @@ > # accesses will go to a given interleave target. Accepted values > # [256, 512, 1k, 2k, 4k, 8k, 16k] > # > +# @device-coherent: Window permits device-coherent (minimally HDM-D) > +# accesses. (since 11.0) Will be at least 11.1 as that's the cycle we are in now I think. > +# > +# @host-only: Window permits host-only coherent (HDM-H) accesses. > +# (since 11.0) > +# > +# @volatile: Window permits volatile memory. (since 11.0) > +# > +# @persistent: Window permits persistent memory. (since 11.0) > +# > +# @fixed-config: Window has a fixed device configuration. Advertised > +# in the CEDT only; not otherwise emulated. (since 11.0) > +# > +# @back-invalidate: Window permits Back-Invalidate (HDM-DB). Implies > +# @device-coherent. (since 11.0) If I read the code above right you check for device coherent. So I'd argue, should say Requires @device_coherent. > +# > # @targets: Target root bridge IDs from -device ...,id=<ID> for each > # root bridge. > # > +# Coherency defaults to host-only coherent; request a device model > +# with @device-coherent or @back-invalidate instead. @volatile and @device-coherent and/or @back-invalidate instead. > +# @persistent are permitted unless set to false, and at least one is > +# required. Clearing @host-only with no device model is rejected, as > +# are host-only coherent + back-invalidate and device-coherent + > +# host-only coherent. > +# > # Since: 7.1 > ## > { 'struct': 'CXLFixedMemoryWindowOptions', > 'data': { > 'size': 'size', > '*interleave-granularity': 'size', > + '*device-coherent': 'bool', > + '*host-only': 'bool', > + '*volatile': 'bool', > + '*persistent': 'bool', > + '*fixed-config': 'bool', > + '*back-invalidate': 'bool', > 'targets': ['str'] }} > > ##
