[PATCH 1/1] virtio-pmem: Support PCI BAR-relative addresses

[tstark@linux.microsoft.com]

From: Taylor Stark <tstark@microsoft.com>

Update the virtio-pmem RFC spec to add support for describing the pmem region
via PCI BARs. Shared memory windows are used to accomplish this, similar to
virtio-fs and virtio-gpu. This is required to support virtio-pmem in Hyper-V,
since Hyper-V only allows PCI devices to operate on memory ranges defined via
BARs.

Signed-off-by: Taylor Stark <tstark@microsoft.com>
---
 virtio-pmem.tex | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/virtio-pmem.tex b/virtio-pmem.tex
index 04e07bb..3f7d48e 100644
--- a/virtio-pmem.tex
+++ b/virtio-pmem.tex
@@ -40,11 +40,21 @@ \subsection{Device Initialization}\label{sec:Device Types / PMEM Device / Device
 Device hotplugs physical memory to guest address space. Persistent memory device
 is emulated with file backed memory at host side.
 
+The device MUST indicate the guest physical address to the driver in one of two
+ways:
 \begin{enumerate}
-\item Guest vpmem start is read from \field{start}.
-\item Guest vpmem end is read from \field{size}.
+\item As a guest absolute address.
+\item As a shared memory region.
 \end{enumerate}
 
+If the guest physical address is indicated as an absolute address, the device
+MUST set \field{start} to the absolute address and \field{size} to the size of
+the address range, in bytes.
+
+If the guest physical address is indicated as a shared memory region, the shared
+memory region MUST be shared memory region ID 0. The device SHOULD set
+\field{start} and \field{size} to zero.
+
 \devicenormative{\subsubsection}{Device Initialization}{Device Types / PMEM Device / Device Initialization}
 
 File backed memory SHOULD be memory mapped to guest address space with SHARED
@@ -52,9 +62,11 @@ \subsection{Device Initialization}\label{sec:Device Types / PMEM Device / Device
 
 \subsection{Driver Initialization}\label{sec:Device Types / PMEM Driver / Driver Initialization}
 
-Driver hotplugs the physical memory and registers associated
-region with the pmem API. Also, configures a flush callback
-function with the corresponding region.
+The driver SHOULD query the physical address ranges where the pmem was mapped.
+When performing the query, the driver MUST first query if shared memory region
+ID 0 is supported by the device. If present, the driver MUST NOT use \field{start}
+or \field{size}. If not present, the driver SHOULD fallback to reading the
+physical address ranges from \field{start} and \field{size}.
 
 \drivernormative{\subsubsection}{Driver Initialization: Filesystem direct access}{Device Types / PMEM Driver / Driver Initialization / Direct access}
 
-- 
2.31.0.vfs.0.1