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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [XEN PATCH v7 14/20] xen/arm: ffa: support guest FFA_PARTITION_INFO_GET
Hi Bertrand,
On Fri, Mar 3, 2023 at 10:51 AM Bertrand Marquis
<Bertrand.Marquis@xxxxxxx> wrote:
>
> Hi Jens,
>
> > On 22 Feb 2023, at 16:33, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> >
> > Adds support in the mediator to handle FFA_PARTITION_INFO_GET requests
> > from a guest. The requests are forwarded to the SPMC and the response is
> > translated according to the FF-A version in use by the guest.
> >
> > Using FFA_PARTITION_INFO_GET changes the owner of the RX buffer to the
> > caller (the guest in this case), so once it is done with the buffer it
> > must be released using FFA_RX_RELEASE before another call can be made.
> >
> > Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> > ---
> > xen/arch/arm/tee/ffa.c | 126 ++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 124 insertions(+), 2 deletions(-)
> >
> > diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> > index 953b6dfd5eca..3571817c0bcd 100644
> > --- a/xen/arch/arm/tee/ffa.c
> > +++ b/xen/arch/arm/tee/ffa.c
> > @@ -141,6 +141,12 @@
> > #define FFA_MSG_POLL 0x8400006AU
> >
> > /* Partition information descriptor */
> > +struct ffa_partition_info_1_0 {
> > + uint16_t id;
> > + uint16_t execution_context;
> > + uint32_t partition_properties;
> > +};
> > +
> > struct ffa_partition_info_1_1 {
> > uint16_t id;
> > uint16_t execution_context;
> > @@ -157,9 +163,8 @@ struct ffa_ctx {
> > uint32_t guest_vers;
> > bool tx_is_mine;
> > bool interrupted;
> > + spinlock_t lock;
> > };
> > -
> > -
>
> This is removing 2 empty lines (previous patch was wrongly adding one)
> but one empty line is required here.
I'll fix it.
>
> > /* Negotiated FF-A version to use with the SPMC */
> > static uint32_t ffa_version __ro_after_init;
> >
> > @@ -173,10 +178,16 @@ static unsigned int subscr_vm_destroyed_count
> > __read_mostly;
> > * Our rx/tx buffers shared with the SPMC.
> > *
> > * ffa_page_count is the number of pages used in each of these buffers.
> > + *
> > + * The RX buffer is protected from concurrent usage with
> > ffa_rx_buffer_lock.
> > + * Note that the SPMC is also tracking the ownership of our RX buffer so
> > + * for calls which uses our RX buffer to deliver a result we must call
> > + * ffa_rx_release() to let the SPMC know that we're done with the buffer.
> > */
> > static void *ffa_rx __read_mostly;
> > static void *ffa_tx __read_mostly;
> > static unsigned int ffa_page_count __read_mostly;
> > +static DEFINE_SPINLOCK(ffa_rx_buffer_lock);
> >
> > static bool ffa_get_version(uint32_t *vers)
> > {
> > @@ -463,6 +474,98 @@ static uint32_t handle_rxtx_unmap(void)
> > return FFA_RET_OK;
> > }
> >
> > +static uint32_t handle_partition_info_get(uint32_t w1, uint32_t w2,
> > uint32_t w3,
> > + uint32_t w4, uint32_t w5,
> > + uint32_t *count)
> > +{
> > + bool query_count_only = w5 & FFA_PARTITION_INFO_GET_COUNT_FLAG;
> > + uint32_t w5_mask = 0;
> > + uint32_t ret = FFA_RET_DENIED;
> > + struct domain *d = current->domain;
> > + struct ffa_ctx *ctx = d->arch.tee;
> > +
> > + /*
> > + * 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_1 )
> > + w5_mask = FFA_PARTITION_INFO_GET_COUNT_FLAG;
> > + if ( w5 & ~w5_mask )
> > + return FFA_RET_INVALID_PARAMETERS;
> > +
> > + if ( query_count_only )
> > + return ffa_partition_info_get(w1, w2, w3, w4, w5, count);
>
> This code seems a bit to complex.
> I would suggest the following:
>
> if (w5 & FFA_PARTITION_INFO_GET_COUNT_FLAG)
> {
> if ( ctx->guest_vers == FFA_VERSION_1_1 )
> return ffa_partition_info_get(w1, w2, w3, w4, w5, count);
> else
> return FFA_RET_INVALID_PARAMETERS;
> }
OK, I can use that. I'll have to add a
if (w5)
return FFA_RET_INVALID_PARAMETERS;
since the rest of the bits must be zero.
>
> > +
> > + if ( !ffa_page_count )
> > + return FFA_RET_DENIED;
> > +
> > + spin_lock(&ctx->lock);
> > + spin_lock(&ffa_rx_buffer_lock);
> > + if ( !ctx->page_count || !ctx->tx_is_mine )
>
> If i understand correctly tx_is_mine is protecting the guest rx
> buffer until rx_release is called by the guest so that we do not
> write in it before the guest has retrieved the data from it.
>
> The name is very misleading, maybe rx_is_writeable or free would be better ?
The FF-A specification talks about ownership of the TX buffer (from
the VMs point of view), hence the name.
I'll change it to rx_is_free to be more intuitive without the spec.
>
> Also it would be more optimal to test it before taking ffa_rx_buffer_lock.
Yes, I'll change that.
>
>
> > + goto out;
> > + ret = ffa_partition_info_get(w1, w2, w3, w4, w5, count);
> > + if ( ret )
> > + goto out;
> > +
> > + if ( ctx->guest_vers == FFA_VERSION_1_0 )
> > + {
> > + size_t n;
> > + struct ffa_partition_info_1_1 *src = ffa_rx;
> > + struct ffa_partition_info_1_0 *dst = ctx->rx;
> > +
> > + if ( ctx->page_count * FFA_PAGE_SIZE < *count * sizeof(*dst) )
> > + {
> > + ret = FFA_RET_NO_MEMORY;
> > + goto out_rx_release;
> > + }
> > +
> > + for ( n = 0; n < *count; n++ )
> > + {
> > + dst[n].id = src[n].id;
> > + dst[n].execution_context = src[n].execution_context;
> > + dst[n].partition_properties = src[n].partition_properties;
> > + }
> > + }
> > + else
> > + {
> > + size_t sz = *count * sizeof(struct ffa_partition_info_1_1);
> > +
> > + if ( ctx->page_count * FFA_PAGE_SIZE < sz )
> > + {
> > + ret = FFA_RET_NO_MEMORY;
> > + goto out_rx_release;
> > + }
> > +
> > +
> > + memcpy(ctx->rx, ffa_rx, sz);
> > + }
> > + ctx->tx_is_mine = false;
>
> at this point we have no reason to hold ctx->lock
ctx->lock is special, we're never supposed to have contention on that
lock. I believe that we in principle could use spin_trylock() instead
and return FFA_RET_BUSY if it fails, but that might be a bit too much.
The VM is supposed to synchronize calls that use the RXTX buffers. So
unlocking ctx->lock early should give nothing for well-behaving
guests, I'd prefer to keep things simple and unlock in reverse order
if you don't mind. I'll add a comment.
>
> > +out_rx_release:
> > + ffa_rx_release();
>
> There should be no case where do release without unlocking.
>
> It might be cleaner to have 2 functions ffa_rx_get and ffa_rx_release
> handling both the lock and the rx_release message.
I'd like to keep ffa_rx_release() as a dumb wrapper. ffa_rx_release()
is also used in init_subscribers() where we don't use any locks.
ffa_rx_release() is called after a successful call to
ffa_partition_info_get() where we also gained ownership of our RX
buffer. Things might be a bit too intertwined for further abstraction.
I'll add a comment explaining the relationship between
ffa_partition_info_get() and ffa_rx_release().
>
> > +out:
> > + spin_unlock(&ffa_rx_buffer_lock);
>
> this should stay with ffa_rx_release
Depending on if you accept my explanation above.
Thanks,
Jens
>
> Cheers
> Bertrand
>
> > + spin_unlock(&ctx->lock);
> > +
> > + return ret;
> > +}
> > +
> > +static uint32_t handle_rx_release(void)
> > +{
> > + uint32_t ret = FFA_RET_DENIED;
> > + struct domain *d = current->domain;
> > + struct ffa_ctx *ctx = d->arch.tee;
> > +
> > + spin_lock(&ctx->lock);
> > + if ( !ctx->page_count || ctx->tx_is_mine )
> > + goto out;
> > + ret = FFA_RET_OK;
> > + ctx->tx_is_mine = true;
> > +out:
> > + spin_unlock(&ctx->lock);
> > +
> > + return ret;
> > +}
> > +
> > static void handle_msg_send_direct_req(struct cpu_user_regs *regs, uint32_t
> > fid)
> > {
> > struct arm_smccc_1_2_regs arg = { .a0 = fid, };
> > @@ -528,6 +631,7 @@ static bool ffa_handle_call(struct cpu_user_regs *regs)
> > uint32_t fid = get_user_reg(regs, 0);
> > struct domain *d = current->domain;
> > struct ffa_ctx *ctx = d->arch.tee;
> > + uint32_t count;
> > int e;
> >
> > if ( !ctx )
> > @@ -559,6 +663,24 @@ static bool ffa_handle_call(struct cpu_user_regs *regs)
> > else
> > set_regs_success(regs, 0, 0);
> > return true;
> > + case FFA_PARTITION_INFO_GET:
> > + e = handle_partition_info_get(get_user_reg(regs, 1),
> > + get_user_reg(regs, 2),
> > + get_user_reg(regs, 3),
> > + get_user_reg(regs, 4),
> > + get_user_reg(regs, 5), &count);
> > + if ( e )
> > + set_regs_error(regs, e);
> > + else
> > + set_regs_success(regs, count, 0);
> > + return true;
> > + case FFA_RX_RELEASE:
> > + e = handle_rx_release();
> > + if ( e )
> > + set_regs_error(regs, e);
> > + else
> > + set_regs_success(regs, 0, 0);
> > + return true;
> > case FFA_MSG_SEND_DIRECT_REQ_32:
> > #ifdef CONFIG_ARM_64
> > case FFA_MSG_SEND_DIRECT_REQ_64:
> > --
> > 2.34.1
> >
>
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