[zion] Add a method for duplicating and scoping down VMMOs.

Use the AHCI section of the PCI config as an example POC of this.

We can now pass a memory capability instead of just the physical
address.

sys/yellowstone/hw/pcie.cpp

@@ -27,8 +27,11 @@ PciReader::PciReader() {
   header_ = PciHeader(vaddr, 0, 0, 0);
 }
 
-uint64_t PciReader::GetAhciPhysical() {
-  return phys_mem_offset_ + achi_device_offset_;
+z_cap_t PciReader::GetAhciVmmo() {
+  uint64_t new_cap;
+  check(ZMemoryObjectDuplicate(gBootPciVmmoCap, achi_device_offset_,
+                               kPcieConfigurationSize, &new_cap));
+  return new_cap;
 }
 
 void PciReader::FunctionDump(uint64_t base, uint64_t bus, uint64_t dev,

sys/yellowstone/hw/pcie.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <stdint.h>
+#include <ztypes.h>
 
 struct PciDeviceHeader {
   uint16_t vendor_id;
@@ -17,16 +18,19 @@ struct PciDeviceHeader {
   uint8_t bist;
 } __attribute__((packed));
 
+// TODO: Figure out if it safe to hardcode this.
+// For the memory mapped access to PCI, it may be true that
+// each configuration item is always the size of a single page.
+const uint64_t kPcieConfigurationSize = 0x1000;
+
 class PciReader {
  public:
   PciReader();
 
-  uint64_t GetAhciPhysical();
+  z_cap_t GetAhciVmmo();
 
  private:
   PciDeviceHeader* header_;
-  // FIXME: Don't hardcode this (It is available from ACPI).
-  uint64_t phys_mem_offset_ = 0xB000'0000;
 
   uint64_t achi_device_offset_ = 0;
 

sys/yellowstone/include/yellowstone.h

@@ -13,7 +13,7 @@ struct YellowstoneGetReq {
 struct YellowstoneGetRegistrationResp {};
 struct YellowstoneGetAhciResp {
   uint64_t type;
-  uint64_t ahci_phys_offset;
+  uint64_t ahci_length;
 };
 
 // Has a denali cap attached.

sys/yellowstone/stub/yellowstone_stub.cpp

@@ -4,12 +4,6 @@
 
 #include "include/yellowstone.h"
 
-namespace {
-
-const uint64_t kPciSize = 0x1000;
-
-}  // namespace
-
 YellowstoneStub::YellowstoneStub(z_cap_t yellowstone_cap)
     : yellowstone_stub_(EndpointClient::AdoptEndpoint(yellowstone_cap)) {}
 
@@ -18,10 +12,10 @@ glcr::ErrorOr<MappedMemoryRegion> YellowstoneStub::GetAhciConfig() {
       .type = kYellowstoneGetAhci,
   };
   ASSIGN_OR_RETURN(
-      YellowstoneGetAhciResp resp,
-      (yellowstone_stub_
-           ->CallEndpoint<YellowstoneGetReq, YellowstoneGetAhciResp>(req)));
-  return MappedMemoryRegion::DirectPhysical(resp.ahci_phys_offset, kPciSize);
+      auto resp_cap_pair,
+      (yellowstone_stub_->CallEndpointGetCap<YellowstoneGetReq,
+                                             YellowstoneGetAhciResp>(req)));
+  return MappedMemoryRegion::FromCapability(resp_cap_pair.second());
 }
 
 glcr::ErrorOr<ScopedDenaliClient> YellowstoneStub::GetDenali() {

sys/yellowstone/yellowstone_server.cpp

@@ -8,6 +8,7 @@
 #include <stdlib.h>
 
 #include "hw/gpt.h"
+#include "hw/pcie.h"
 #include "include/yellowstone.h"
 
 namespace {
@@ -55,9 +56,11 @@ glcr::ErrorCode YellowstoneServer::HandleRequest(RequestContext& request,
       dbgln("Yellowstone::GetAHCI");
       YellowstoneGetAhciResp resp{
           .type = kYellowstoneGetAhci,
-          .ahci_phys_offset = pci_reader_.GetAhciPhysical(),
+          .ahci_length = kPcieConfigurationSize,
       };
-      RET_ERR(response.WriteStruct<YellowstoneGetAhciResp>(resp));
+      z_cap_t vmmo_cap = pci_reader_.GetAhciVmmo();
+      RET_ERR(
+          response.WriteStructWithCap<YellowstoneGetAhciResp>(resp, vmmo_cap));
       break;
     }
     case kYellowstoneGetRegistration: {