[PATCH v2 10/10] KVM: arm64: pkvm: Add support for fragmented FF-A descriptors

Will Deacon
2023-04-19T12:22:52Z

From: Quentin Perret <qperret@google.com>

FF-A memory descriptors may need to be sent in fragments when they don't
fit in the mailboxes. Doing so involves using the FRAG_TX and FRAG_RX
primitives defined in the FF-A protocol.

Add support in the pKVM FF-A relayer for fragmented descriptors by
monitoring outgoing FRAG_TX transactions and by buffering large
descriptors on the reclaim path.

Co-developed-by: Andrew Walbran <qwandor@google.com>
Signed-off-by: Andrew Walbran <qwandor@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_pkvm.h | 17 ++-
arch/arm64/kvm/hyp/nvhe/ffa.c | 170 ++++++++++++++++++++++++++----
2 files changed, 162 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
index 2b495ec59deb..e46250a02017 100644
--- a/arch/arm64/include/asm/kvm_pkvm.h
+++ b/arch/arm64/include/asm/kvm_pkvm.h
@@ -6,7 +6,9 @@
#ifndef __ARM64_KVM_PKVM_H__
#define __ARM64_KVM_PKVM_H__

+#include <linux/arm_ffa.h>
#include <linux/memblock.h>
+#include <linux/scatterlist.h>
#include <asm/kvm_pgtable.h>

/* Maximum number of VMs that can co-exist under pKVM. */
@@ -110,8 +112,19 @@ static inline unsigned long host_s2_pgtable_pages(void)

static inline unsigned long hyp_ffa_proxy_pages(void)
{
- /* A page each for the hypervisor's RX and TX mailboxes. */
- return 2 * KVM_FFA_MBOX_NR_PAGES;
+ size_t desc_max;
+
+ /*
+ * The hypervisor FFA proxy needs enough memory to buffer a fragmented
+ * descriptor returned from EL3 in response to a RETRIEVE_REQ call.
+ */
+ desc_max = sizeof(struct ffa_mem_region) +
+ sizeof(struct ffa_mem_region_attributes) +
+ sizeof(struct ffa_composite_mem_region) +
+ SG_MAX_SEGMENTS * sizeof(struct ffa_mem_region_addr_range);
+
+ /* Plus a page each for the hypervisor's RX and TX mailboxes. */
+ return (2 * KVM_FFA_MBOX_NR_PAGES) + DIV_ROUND_UP(desc_max, PAGE_SIZE);
}

#endif /* __ARM64_KVM_PKVM_H__ */
diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index aa8bfc97a164..a787f9134c39 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -42,6 +42,18 @@
*/
#define HOST_FFA_ID 0

+/*
+ * A buffer to hold the maximum descriptor size we can see from the host,
+ * which is required when the SPMD returns a fragmented FFA_MEM_RETRIEVE_RESP
+ * when resolving the handle on the reclaim path.
+ */
+struct kvm_ffa_descriptor_buffer {
+ void *buf;
+ size_t len;
+};
+
+static struct kvm_ffa_descriptor_buffer ffa_desc_buf;
+
struct kvm_ffa_buffers {
hyp_spinlock_t lock;
void *tx;
@@ -122,6 +134,24 @@ static int spmd_unmap_ffa_buffers(void)
return res.a0 == FFA_SUCCESS ? FFA_RET_SUCCESS : res.a2;
}

+static void spmd_mem_frag_tx(struct arm_smccc_res *res, u32 handle_lo,
+ u32 handle_hi, u32 fraglen, u32 endpoint_id)
+{
+ arm_smccc_1_1_smc(FFA_MEM_FRAG_TX,
+ handle_lo, handle_hi, fraglen, endpoint_id,
+ 0, 0, 0,
+ res);
+}
+
+static void spmd_mem_frag_rx(struct arm_smccc_res *res, u32 handle_lo,
+ u32 handle_hi, u32 fragoff)
+{
+ arm_smccc_1_1_smc(FFA_MEM_FRAG_RX,
+ handle_lo, handle_hi, fragoff, HOST_FFA_ID,
+ 0, 0, 0,
+ res);
+}
+
static void spmd_mem_xfer(struct arm_smccc_res *res, u64 func_id, u32 len,
u32 fraglen)
{
@@ -323,6 +353,64 @@ static int ffa_host_unshare_ranges(struct ffa_mem_region_addr_range *ranges,
return ret;
}

+static void do_ffa_mem_frag_tx(struct arm_smccc_res *res,
+ struct kvm_cpu_context *ctxt)
+{
+ DECLARE_REG(u32, handle_lo, ctxt, 1);
+ DECLARE_REG(u32, handle_hi, ctxt, 2);
+ DECLARE_REG(u32, fraglen, ctxt, 3);
+ DECLARE_REG(u32, endpoint_id, ctxt, 4);
+ struct ffa_mem_region_addr_range *buf;
+ int ret = FFA_RET_INVALID_PARAMETERS;
+ u32 nr_ranges;
+
+ if (fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE)
+ goto out;
+
+ if (fraglen % sizeof(*buf))
+ goto out;
+
+ hyp_spin_lock(&host_buffers.lock);
+ if (!host_buffers.tx)
+ goto out_unlock;
+
+ buf = hyp_buffers.tx;
+ memcpy(buf, host_buffers.tx, fraglen);
+ nr_ranges = fraglen / sizeof(*buf);
+
+ ret = ffa_host_share_ranges(buf, nr_ranges);
+ if (ret) {
+ /*
+ * We're effectively aborting the transaction, so we need
+ * to restore the global state back to what it was prior to
+ * transmission of the first fragment.
+ */
+ spmd_mem_reclaim(res, handle_lo, handle_hi, 0);
+ WARN_ON(res->a0 != FFA_SUCCESS);
+ goto out_unlock;
+ }
+
+ spmd_mem_frag_tx(res, handle_lo, handle_hi, fraglen, endpoint_id);
+ if (res->a0 != FFA_SUCCESS && res->a0 != FFA_MEM_FRAG_RX)
+ WARN_ON(ffa_host_unshare_ranges(buf, nr_ranges));
+
+out_unlock:
+ hyp_spin_unlock(&host_buffers.lock);
+out:
+ if (ret)
+ ffa_to_smccc_res(res, ret);
+
+ /*
+ * If for any reason this did not succeed, we're in trouble as we have
+ * now lost the content of the previous fragments and we can't rollback
+ * the host stage-2 changes. The pages previously marked as shared will
+ * remain stuck in that state forever, hence preventing the host from
+ * sharing/donating them again and may possibly lead to subsequent
+ * failures, but this will not compromise confidentiality.
+ */
+ return;
+}
+
static __always_inline void do_ffa_mem_xfer(const u64 func_id,
struct arm_smccc_res *res,
struct kvm_cpu_context *ctxt)
@@ -333,8 +421,8 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
DECLARE_REG(u32, npages_mbz, ctxt, 4);
struct ffa_composite_mem_region *reg;
struct ffa_mem_region *buf;
+ u32 offset, nr_ranges;
int ret = 0;
- u32 offset;

BUILD_BUG_ON(func_id != FFA_FN64_MEM_SHARE &&
func_id != FFA_FN64_MEM_LEND);
@@ -345,11 +433,6 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
goto out;
}

- if (fraglen < len) {
- ret = FFA_RET_ABORTED;
- goto out;
- }
-
if (fraglen < sizeof(struct ffa_mem_region) +
sizeof(struct ffa_mem_region_attributes)) {
ret = FFA_RET_INVALID_PARAMETERS;
@@ -377,21 +460,26 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
}

reg = (void *)buf + offset;
- if (fraglen < offset + sizeof(struct ffa_composite_mem_region) +
- reg->addr_range_cnt *
- sizeof(struct ffa_mem_region_addr_range)) {
+ nr_ranges = ((void *)buf + fraglen) - (void *)reg->constituents;
+ if (nr_ranges % sizeof(reg->constituents[0])) {
ret = FFA_RET_INVALID_PARAMETERS;
goto out_unlock;
}

- ret = ffa_host_share_ranges(reg->constituents, reg->addr_range_cnt);
+ nr_ranges /= sizeof(reg->constituents[0]);
+ ret = ffa_host_share_ranges(reg->constituents, nr_ranges);
if (ret)
goto out_unlock;

spmd_mem_xfer(res, func_id, len, fraglen);
- if (res->a0 != FFA_SUCCESS) {
- WARN_ON(ffa_host_unshare_ranges(reg->constituents,
- reg->addr_range_cnt));
+ if (fraglen != len) {
+ if (res->a0 != FFA_MEM_FRAG_RX)
+ goto err_unshare;
+
+ if (res->a3 != fraglen)
+ goto err_unshare;
+ } else if (res->a0 != FFA_SUCCESS) {
+ goto err_unshare;
}

out_unlock:
@@ -400,6 +488,10 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
if (ret)
ffa_to_smccc_res(res, ret);
return;
+
+err_unshare:
+ WARN_ON(ffa_host_unshare_ranges(reg->constituents, nr_ranges));
+ goto out_unlock;
}

static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
@@ -409,9 +501,9 @@ static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
DECLARE_REG(u32, handle_hi, ctxt, 2);
DECLARE_REG(u32, flags, ctxt, 3);
struct ffa_composite_mem_region *reg;
+ u32 offset, len, fraglen, fragoff;
struct ffa_mem_region *buf;
int ret = 0;
- u32 offset;
u64 handle;

handle = PACK_HANDLE(handle_lo, handle_hi);
@@ -429,11 +521,8 @@ static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
if (res->a0 != FFA_MEM_RETRIEVE_RESP)
goto out_unlock;

- /* Check for fragmentation */
- if (res->a1 != res->a2) {
- ret = FFA_RET_ABORTED;
- goto out_unlock;
- }
+ len = res->a1;
+ fraglen = res->a2;

offset = buf->ep_mem_access[0].composite_off;
/*
@@ -441,16 +530,36 @@ static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
* check that we end up with something that doesn't look _completely_
* bogus.
*/
- if (WARN_ON(offset > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE)) {
+ if (WARN_ON(offset > len ||
+ fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE)) {
ret = FFA_RET_ABORTED;
goto out_unlock;
}

- reg = (void *)buf + offset;
+ if (len > ffa_desc_buf.len) {
+ ret = FFA_RET_NO_MEMORY;
+ goto out_unlock;
+ }
+
+ buf = ffa_desc_buf.buf;
+ memcpy(buf, hyp_buffers.rx, fraglen);
+
+ for (fragoff = fraglen; fragoff < len; fragoff += fraglen) {
+ spmd_mem_frag_rx(res, handle_lo, handle_hi, fragoff);
+ if (res->a0 != FFA_MEM_FRAG_TX) {
+ ret = FFA_RET_INVALID_PARAMETERS;
+ goto out_unlock;
+ }
+
+ fraglen = res->a3;
+ memcpy((void *)buf + fragoff, hyp_buffers.rx, fraglen);
+ }
+
spmd_mem_reclaim(res, handle_lo, handle_hi, flags);
if (res->a0 != FFA_SUCCESS)
goto out_unlock;

+ reg = (void *)buf + offset;
/* If the SPMD was happy, then we should be too. */
WARN_ON(ffa_host_unshare_ranges(reg->constituents,
reg->addr_range_cnt));
@@ -552,6 +661,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt)
case FFA_FN64_MEM_LEND:
do_ffa_mem_xfer(FFA_FN64_MEM_LEND, &res, host_ctxt);
goto out_handled;
+ case FFA_MEM_FRAG_TX:
+ do_ffa_mem_frag_tx(&res, host_ctxt);
+ goto out_handled;
}

if (ffa_call_supported(func_id))
@@ -567,6 +679,7 @@ int hyp_ffa_init(void *pages)
{
struct arm_smccc_res res;
size_t min_rxtx_sz;
+ void *tx, *rx;

if (kvm_host_psci_config.smccc_version < ARM_SMCCC_VERSION_1_2)
return 0;
@@ -607,10 +720,21 @@ int hyp_ffa_init(void *pages)
if (min_rxtx_sz > PAGE_SIZE)
return -EOPNOTSUPP;

+ tx = pages;
+ pages += KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE;
+ rx = pages;
+ pages += KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE;
+
+ ffa_desc_buf = (struct kvm_ffa_descriptor_buffer) {
+ .buf = pages,
+ .len = PAGE_SIZE *
+ (hyp_ffa_proxy_pages() - (2 * KVM_FFA_MBOX_NR_PAGES)),
+ };
+
hyp_buffers = (struct kvm_ffa_buffers) {
.lock = __HYP_SPIN_LOCK_UNLOCKED,
- .tx = pages,
- .rx = pages + (KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE),
+ .tx = tx,
+ .rx = rx,
};

host_buffers = (struct kvm_ffa_buffers) {