From 3eaeba4b5585ef5f8b98563f38de0bbceed3523d Mon Sep 17 00:00:00 2001
From: Jose Carlos Venegas Munoz <jose.carlos.venegas.munoz@intel.com>
Date: Wed, 22 Apr 2020 23:10:31 +0000
Subject: [PATCH] vm-virtio: Fix FS_IO callback for virtio-fs

FS_IO is part of the actions a vhost-user-fs daemon can ask the VMM to
perform on its behalf. It is meant to read/write the content from a file
descriptor directly into a guest memory region. This region can either
be a RAM region or the dedicated cache region for virtio-fs.

The way FS_IO was implemented, it was only expecting the guest physical
address provided through the "cache_offset" field to refer to the cache
region. Unfortunately, this was only implementing FS_IO partially.

This patch extends the existing FS_IO implementation by checking the GPA
against the cache region as a first step, but if it is not part of the
cache region address range, then we fallback onto searching for a RAM
region that could match. If there is a matching RAM region, we retrieve
the corresponding host address to let the VMM read/write from/to it.

Fixes: #1054

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Signed-off-by: Jose Carlos Venegas Munoz <jose.carlos.venegas.munoz@intel.com>
---
 vm-virtio/src/vhost_user/fs.rs | 40 ++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/vm-virtio/src/vhost_user/fs.rs b/vm-virtio/src/vhost_user/fs.rs
index e8debdf5e..6dbde8afa 100644
--- a/vm-virtio/src/vhost_user/fs.rs
+++ b/vm-virtio/src/vhost_user/fs.rs
@@ -27,8 +27,8 @@ use vhost_rs::vhost_user::{
 };
 use vhost_rs::VhostBackend;
 use vm_memory::{
-    Address, ByteValued, GuestAddress, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap,
-    MmapRegion,
+    Address, ByteValued, GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic,
+    GuestMemoryMmap, MmapRegion,
 };
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;
@@ -39,6 +39,7 @@ struct SlaveReqHandler {
     cache_offset: GuestAddress,
     cache_size: u64,
     mmap_cache_addr: u64,
+    mem: GuestMemoryAtomic<GuestMemoryMmap>,
 }
 
 impl SlaveReqHandler {
@@ -183,18 +184,32 @@ impl VhostUserMasterReqHandler for SlaveReqHandler {
             let cache_end = self.cache_offset.raw_value() + self.cache_size;
             let efault = libc::EFAULT;
 
-            let offset = gpa
-                .checked_sub(self.cache_offset.raw_value())
-                .ok_or_else(|| io::Error::from_raw_os_error(efault))?;
-            let end = gpa
-                .checked_add(fs.len[i])
-                .ok_or_else(|| io::Error::from_raw_os_error(efault))?;
+            let mut ptr = if gpa >= self.cache_offset.raw_value() && gpa < cache_end {
+                let offset = gpa
+                    .checked_sub(self.cache_offset.raw_value())
+                    .ok_or_else(|| io::Error::from_raw_os_error(efault))?;
+                let end = gpa
+                    .checked_add(fs.len[i])
+                    .ok_or_else(|| io::Error::from_raw_os_error(efault))?;
 
-            if gpa < self.cache_offset.raw_value() || gpa >= cache_end || end >= cache_end {
-                return Err(io::Error::from_raw_os_error(efault));
-            }
+                if end >= cache_end {
+                    return Err(io::Error::from_raw_os_error(efault));
+                }
+
+                self.mmap_cache_addr + offset
+            } else {
+                self.mem
+                    .memory()
+                    .get_host_address(GuestAddress(gpa))
+                    .map_err(|e| {
+                        error!(
+                            "Failed to find RAM region associated with guest physical address 0x{:x}: {:?}",
+                            gpa, e
+                        );
+                        io::Error::from_raw_os_error(efault)
+                    })? as u64
+            };
 
-            let mut ptr = self.mmap_cache_addr + offset;
             while len > 0 {
                 let ret = if (fs.flags[i] & VhostUserFSSlaveMsgFlags::MAP_W)
                     == VhostUserFSSlaveMsgFlags::MAP_W
@@ -479,6 +494,7 @@ impl VirtioDevice for Fs {
                     cache_offset: cache.0.addr,
                     cache_size: cache.0.len,
                     mmap_cache_addr: cache.0.host_addr,
+                    mem,
                 }));
 
                 let req_handler = MasterReqHandler::new(vu_master_req_handler).map_err(|e| {