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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v1 02/12] xen/arm: ffa: per-VM FFA_VERSION negotiation state
Track FF-A version negotiation per VM and enforce that no FF-A ABI
(other than FFA_VERSION) is processed before a guest has selected a
version.
Each ffa_ctx gains a dedicated guest_vers_lock, a negotiated version
(guest_vers) and a guest_vers_tmp:
- guest_vers is the version negotiated or 0 if no version has been
negotiated. This must be used with ACCESS_ONCE when reading it without
the spinlock taken.
- guest_vers_tmp stores the version currently requested by a VM.
The version requested is the one actually negotiated once a call
different from FFA_VERSION is done to allow several attempts and as
requested by FF-A specification.
We always return our implementation version FFA_MY_VERSION, even if the
version requested was different, as requested by FF-A specification.
Any call other than FFA_VERSION is rejected until a version has been
requested.
Update all places in the code where guest_vers is used to use
ACCESS_ONCE.
This prevents partially initialised contexts from using the mediator
and complies with the FF-A 1.2 FFA_VERSION semantics.
Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
---
Changes in v1:
- remove the guest_vers_negotiated and use guest_vers = 0 as condition
for a version being negotiated instead
- introduce guest_vers_tmp to store a requested version until it is
becoming the one negotiated.
- remove not needed if negotiated condition.
- use ACCESS_ONCE when reading guest_vers and use guest_vers == 0 as
condition for a version being negotiated.
- Update FF-A version handling comment in ffa_private.h
---
xen/arch/arm/tee/ffa.c | 101 +++++++++++++++++++++++++-------
xen/arch/arm/tee/ffa_msg.c | 2 +-
xen/arch/arm/tee/ffa_partinfo.c | 4 +-
xen/arch/arm/tee/ffa_private.h | 26 ++++++--
xen/arch/arm/tee/ffa_shm.c | 3 +-
5 files changed, 105 insertions(+), 31 deletions(-)
diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
index 2b4e24750d52..aadd6c21e7f2 100644
--- a/xen/arch/arm/tee/ffa.c
+++ b/xen/arch/arm/tee/ffa.c
@@ -158,31 +158,38 @@ static bool ffa_abi_supported(uint32_t id)
return !ffa_simple_call(FFA_FEATURES, id, 0, 0, 0);
}
-static void handle_version(struct cpu_user_regs *regs)
+static bool ffa_negotiate_version(struct cpu_user_regs *regs)
{
struct domain *d = current->domain;
struct ffa_ctx *ctx = d->arch.tee;
- uint32_t vers = get_user_reg(regs, 1);
- uint32_t old_vers;
+ uint32_t fid = get_user_reg(regs, 0);
+ uint32_t in_vers = get_user_reg(regs, 1);
+ uint32_t out_vers = FFA_MY_VERSION;
- /*
- * Guest will use the version it requested if it is our major and minor
- * lower or equals to ours. If the minor is greater, our version will be
- * used.
- * In any case return our version to the caller.
- */
- if ( FFA_VERSION_MAJOR(vers) == FFA_MY_VERSION_MAJOR )
+ spin_lock(&ctx->guest_vers_lock);
+
+ /* If negotiation already published, continue without handling. */
+ if ( ACCESS_ONCE(ctx->guest_vers) )
+ goto out_continue;
+
+ if ( fid != FFA_VERSION )
{
- spin_lock(&ctx->lock);
- old_vers = ctx->guest_vers;
+ if ( !ctx->guest_vers_tmp )
+ {
+ out_vers = 0;
+ goto out_handled;
+ }
- if ( FFA_VERSION_MINOR(vers) > FFA_MY_VERSION_MINOR )
- ctx->guest_vers = FFA_MY_VERSION;
- else
- ctx->guest_vers = vers;
- spin_unlock(&ctx->lock);
+ /*
+ * A successful FFA_VERSION call does not freeze negotiation. Guests
+ * are allowed to issue multiple FFA_VERSION attempts (e.g. probing
+ * several minor versions). Negotiation becomes final only when a
+ * non-VERSION ABI is invoked, as required by the FF-A specification.
+ * Finalize negotiation: publish guest_vers once, then never change.
+ */
+ ACCESS_ONCE(ctx->guest_vers) = ctx->guest_vers_tmp;
- if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) && !old_vers )
+ if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) )
{
/* One more VM with FF-A support available */
inc_ffa_vm_count();
@@ -190,8 +197,48 @@ static void handle_version(struct cpu_user_regs *regs)
list_add_tail(&ctx->ctx_list, &ffa_ctx_head);
write_unlock(&ffa_ctx_list_rwlock);
}
+
+ goto out_continue;
}
- ffa_set_regs(regs, FFA_MY_VERSION, 0, 0, 0, 0, 0, 0, 0);
+
+ /*
+ * guest_vers_tmp stores the version selected by the guest (lower minor may
+ * require reduced data structures). However, the value returned to the
+ * guest via FFA_VERSION is always FFA_MY_VERSION, the implementation
+ * version, as required by FF-A. The two values intentionally differ.
+ */
+
+ /*
+ * Return our highest implementation version on request different than our
+ * major and mark negotiated version as our implementation version.
+ */
+ if ( FFA_VERSION_MAJOR(in_vers) != FFA_MY_VERSION_MAJOR )
+ {
+ ctx->guest_vers_tmp = FFA_MY_VERSION;
+ goto out_handled;
+ }
+
+ /*
+ * Use our minor version if a greater minor was requested or the requested
+ * minor if it is lower than ours was requested.
+ */
+ if ( FFA_VERSION_MINOR(in_vers) > FFA_MY_VERSION_MINOR )
+ ctx->guest_vers_tmp = FFA_MY_VERSION;
+ else
+ ctx->guest_vers_tmp = in_vers;
+
+out_handled:
+ spin_unlock(&ctx->guest_vers_lock);
+ if ( out_vers )
+ ffa_set_regs(regs, out_vers, 0, 0, 0, 0, 0, 0, 0);
+ else
+ ffa_set_regs_error(regs, FFA_RET_NOT_SUPPORTED);
+ return true;
+
+out_continue:
+ spin_unlock(&ctx->guest_vers_lock);
+
+ return false;
}
static void handle_features(struct cpu_user_regs *regs)
@@ -274,10 +321,17 @@ static bool ffa_handle_call(struct cpu_user_regs *regs)
if ( !ctx )
return false;
+ /* A version must be negotiated first */
+ if ( !ACCESS_ONCE(ctx->guest_vers) )
+ {
+ if ( ffa_negotiate_version(regs) )
+ return true;
+ }
+
switch ( fid )
{
case FFA_VERSION:
- handle_version(regs);
+ ffa_set_regs(regs, FFA_MY_VERSION, 0, 0, 0, 0, 0, 0, 0);
return true;
case FFA_ID_GET:
ffa_set_regs_success(regs, ffa_get_vm_id(d), 0);
@@ -371,6 +425,11 @@ static int ffa_domain_init(struct domain *d)
d->arch.tee = ctx;
ctx->teardown_d = d;
INIT_LIST_HEAD(&ctx->shm_list);
+ spin_lock_init(&ctx->lock);
+ spin_lock_init(&ctx->guest_vers_lock);
+ ctx->guest_vers = 0;
+ ctx->guest_vers_tmp = 0;
+ INIT_LIST_HEAD(&ctx->ctx_list);
ctx->ffa_id = ffa_get_vm_id(d);
ctx->num_vcpus = d->max_vcpus;
@@ -452,7 +511,7 @@ static int ffa_domain_teardown(struct domain *d)
if ( !ctx )
return 0;
- if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) && ctx->guest_vers )
+ if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) && ACCESS_ONCE(ctx->guest_vers) )
{
dec_ffa_vm_count();
write_lock(&ffa_ctx_list_rwlock);
diff --git a/xen/arch/arm/tee/ffa_msg.c b/xen/arch/arm/tee/ffa_msg.c
index c20c5bec0f76..2c2ebc9c5cd6 100644
--- a/xen/arch/arm/tee/ffa_msg.c
+++ b/xen/arch/arm/tee/ffa_msg.c
@@ -113,7 +113,7 @@ static int32_t ffa_msg_send2_vm(uint16_t dst_id, const void
*src_buf,
}
dst_ctx = dst_d->arch.tee;
- if ( !dst_ctx->guest_vers )
+ if ( !ACCESS_ONCE(dst_ctx->guest_vers) )
{
ret = FFA_RET_INVALID_PARAMETERS;
goto out_unlock;
diff --git a/xen/arch/arm/tee/ffa_partinfo.c b/xen/arch/arm/tee/ffa_partinfo.c
index fa56b1587e3b..ec5a53ed1cab 100644
--- a/xen/arch/arm/tee/ffa_partinfo.c
+++ b/xen/arch/arm/tee/ffa_partinfo.c
@@ -238,7 +238,7 @@ void ffa_handle_partition_info_get(struct cpu_user_regs
*regs)
* use the v1.0 structure size in the destination buffer.
* Otherwise use the size of the highest version we support, here 1.1.
*/
- if ( ctx->guest_vers == FFA_VERSION_1_0 )
+ if ( ACCESS_ONCE(ctx->guest_vers) == FFA_VERSION_1_0 )
dst_size = sizeof(struct ffa_partition_info_1_0);
else
dst_size = sizeof(struct ffa_partition_info_1_1);
@@ -250,7 +250,7 @@ void ffa_handle_partition_info_get(struct cpu_user_regs
*regs)
* FF-A v1.0 has w5 MBZ while v1.1 allows
* FFA_PARTITION_INFO_GET_COUNT_FLAG to be non-zero.
*/
- if ( ctx->guest_vers == FFA_VERSION_1_0 ||
+ if ( ACCESS_ONCE(ctx->guest_vers) == FFA_VERSION_1_0 ||
flags != FFA_PARTITION_INFO_GET_COUNT_FLAG )
{
ret = FFA_RET_INVALID_PARAMETERS;
diff --git a/xen/arch/arm/tee/ffa_private.h b/xen/arch/arm/tee/ffa_private.h
index 8d01da0009d3..4e4ac7fd7bc4 100644
--- a/xen/arch/arm/tee/ffa_private.h
+++ b/xen/arch/arm/tee/ffa_private.h
@@ -355,12 +355,6 @@ struct ffa_ctx {
* Global data accessed with lock locked.
*/
spinlock_t lock;
- /*
- * FF-A version negotiated by the guest, only modifications to
- * this field are done with the lock held as this is expected to
- * be done once at init by a guest.
- */
- uint32_t guest_vers;
/* Number of 4kB pages in each of rx/rx_pg and tx/tx_pg */
unsigned int page_count;
/* Number of allocated shared memory object */
@@ -368,6 +362,26 @@ struct ffa_ctx {
/* Used shared memory objects, struct ffa_shm_mem */
struct list_head shm_list;
+ /*
+ * FF-A version handling
+ * guest_vers is the single published negotiated version. It is 0 until
+ * negotiation completes, after which it is set once and never changes.
+ * Negotiation uses guest_vers_tmp under guest_vers_lock; when a
+ * non-VERSION ABI is invoked, Xen finalizes negotiation by publishing
+ * guest_vers using ACCESS_ONCE() store.
+ * Readers use ACCESS_ONCE(guest_vers) != 0 to detect availability and
+ * can consume guest_vers without barriers because it never changes once
+ * published.
+ */
+ spinlock_t guest_vers_lock;
+ /*
+ * Published negotiated version. Zero means "not negotiated yet".
+ * Once non-zero, it never changes.
+ */
+ uint32_t guest_vers;
+ /* Temporary version used during negotiation under guest_vers_lock */
+ uint32_t guest_vers_tmp;
+
/*
* Rx buffer, accessed with rx_lock locked.
* rx_is_free is used to serialize access.
diff --git a/xen/arch/arm/tee/ffa_shm.c b/xen/arch/arm/tee/ffa_shm.c
index d628c1b70609..dad3da192247 100644
--- a/xen/arch/arm/tee/ffa_shm.c
+++ b/xen/arch/arm/tee/ffa_shm.c
@@ -495,7 +495,8 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs)
if ( frag_len > ctx->page_count * FFA_PAGE_SIZE )
goto out_unlock;
- ret = read_mem_transaction(ctx->guest_vers, ctx->tx, frag_len, &trans);
+ ret = read_mem_transaction(ACCESS_ONCE(ctx->guest_vers), ctx->tx,
+ frag_len, &trans);
if ( ret )
goto out_unlock;
--
2.51.2
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