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Re: [PATCH V4 14/24] arm/ioreq: Introduce arch specific bits for IOREQ/DM features

Hi Julien

          ret = relinquish_memory(d, &d->xenpage_list);
          if ( ret )
diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
index ae7ef96..9814481 100644
--- a/xen/arch/arm/io.c
+++ b/xen/arch/arm/io.c
@@ -16,6 +16,7 @@
   * GNU General Public License for more details.
  +#include <xen/ioreq.h>
  #include <xen/lib.h>
  #include <xen/spinlock.h>
  #include <xen/sched.h>
@@ -23,6 +24,7 @@
  #include <asm/cpuerrata.h>
  #include <asm/current.h>
  #include <asm/mmio.h>
+#include <asm/hvm/ioreq.h>

Shouldn't this have been included by "xen/ioreq.h"?
Well, for V1 asm/hvm/ioreq.h was included by xen/ioreq.h. But, it turned out that there was nothing inside common header required arch one to be included and I was asked to include arch header where it was indeed needed (several *.c files).

Fair enough.


If you return IO_HANDLED here, then it means the we will take care of previous I/O but the current one is going to be ignored.
Which current one? As I understand, if try_fwd_ioserv() gets called with vio->req.state == STATE_IORESP_READY then this is a second round after emulator completes the emulation (the first round was when we returned IO_RETRY down the function and claimed that we would need a completion), so we are still dealing with previous I/O. vcpu_ioreq_handle_completion() -> arch_ioreq_complete_mmio() -> try_handle_mmio() -> try_fwd_ioserv() -> handle_ioserv() And after we return IO_HANDLED here, handle_ioserv() will be called to complete the handling of this previous I/O emulation.
Or I really missed something?

Hmmm... I somehow thought try_fw_ioserv() would only be called the first time. Do you have a branch with your code applied? This would help to follow the different paths.
Yes, I mentioned about it in cover letter.

Please see
why 5 - because I started counting from the RFC)

Oh, I looked at the cover letter and didn't find it. Hence why I asked. I should have looked more carefully. Thanks!

I have looked closer at the question and I am not sure to understand why arch_ioreq_complete_mmio() is going to call try_handle_mmio().

This looks pretty innefficient to me because we already now the IO was handled by the IOREQ server.

I realize that x86 is calling handle_mmio() again. However, I don't think we need the same on Arm because the instruction for accessing device memory are a lot simpler (you can only read or store at most a 64-bit value).

I think, I agree.

So I would like to keep our emulation simple and not rely on try_ioserv_fw() to always return true when call from completion (AFAICT it is not possible to return false then).

So what you are proposing is just a replacement try_ioserv_fw() by handle_ioserv() technically?

diff --git a/xen/arch/arm/ioreq.c b/xen/arch/arm/ioreq.c
index 40b9e59..0508bd8 100644
--- a/xen/arch/arm/ioreq.c
+++ b/xen/arch/arm/ioreq.c
@@ -101,12 +101,10 @@ enum io_state try_fwd_ioserv(struct cpu_user_regs *regs,

 bool arch_ioreq_complete_mmio(void)
-    struct vcpu *v = current;
     struct cpu_user_regs *regs = guest_cpu_user_regs();
     const union hsr hsr = { .bits = regs->hsr };
-    paddr_t addr = v->io.req.addr;

-    if ( try_handle_mmio(regs, hsr, addr) == IO_HANDLED )
+    if ( handle_ioserv(regs, current) == IO_HANDLED )
         advance_pc(regs, hsr);
         return true;

I will answer to the rest separately.

Thank you.



Oleksandr Tyshchenko



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