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Mon, 10 Aug 2020 06:41:38 -0700 (PDT) Received: from [192.168.1.2] ([212.22.223.21]) by smtp.gmail.com with ESMTPSA id g6sm10751454lfr.51.2020.08.10.06.41.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Aug 2020 06:41:37 -0700 (PDT) Subject: Re: [RFC PATCH V1 01/12] hvm/ioreq: Make x86's IOREQ feature common From: Oleksandr To: Stefano Stabellini , Julien Grall References: <1596478888-23030-1-git-send-email-olekstysh@gmail.com> <1596478888-23030-2-git-send-email-olekstysh@gmail.com> <000c01d66a33$2bd56510$83802f30$@xen.org> <9f83a7ed-ca97-449f-c7b9-a1140644abe9@gmail.com> <2ab4c567-8efa-1b9d-ab00-4ea7e1ab323e@suse.com> <013b142d-5296-5bbe-7d19-903f59e0c974@gmail.com> <06f78323-b8f5-fd11-486a-437267eccc29@gmail.com> Message-ID: <27513b2b-e59b-d446-7e68-eac4bc503409@gmail.com> Date: Mon, 10 Aug 2020 16:41:31 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <06f78323-b8f5-fd11-486a-437267eccc29@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: 'Kevin Tian' , 'Jun Nakajima' , 'Wei Liu' , paul@xen.org, 'Andrew Cooper' , 'Ian Jackson' , 'George Dunlap' , 'Tim Deegan' , 'Oleksandr Tyshchenko' , 'Julien Grall' , Jan Beulich , xen-devel@lists.xenproject.org, =?UTF-8?B?J1JvZ2VyIFBhdSBNb25uw6kn?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Hi On 08.08.20 01:19, Oleksandr wrote: > > On 08.08.20 00:50, Stefano Stabellini wrote: > > Hi Stefano > >> On Fri, 7 Aug 2020, Oleksandr wrote: >>> On 06.08.20 03:37, Stefano Stabellini wrote: >>> >>> Hi Stefano >>> >>> Trying to simulate IO_RETRY handling mechanism (according to model >>> below) I >>> continuously get IO_RETRY from try_fwd_ioserv() ... >>> >>>> OK, thanks for the details. My interpretation seems to be correct. >>>> >>>> In which case, it looks like xen/arch/arm/io.c:try_fwd_ioserv should >>>> return IO_RETRY. Then, xen/arch/arm/traps.c:do_trap_stage2_abort_guest >>>> also needs to handle try_handle_mmio returning IO_RETRY the first >>>> around, and IO_HANDLED when after QEMU does its job. >>>> >>>> What should do_trap_stage2_abort_guest do on IO_RETRY? Simply return >>>> early and let the scheduler do its job? Something like: >>>> >>>>               enum io_state state = try_handle_mmio(regs, hsr, gpa); >>>> >>>>               switch ( state ) >>>>               { >>>>               case IO_ABORT: >>>>                   goto inject_abt; >>>>               case IO_HANDLED: >>>>                   advance_pc(regs, hsr); >>>>                   return; >>>>               case IO_RETRY: >>>>                   /* finish later */ >>>>                   return; >>>>               case IO_UNHANDLED: >>>>                   /* IO unhandled, try another way to handle it. */ >>>>                   break; >>>>               default: >>>>                   ASSERT_UNREACHABLE(); >>>>               } >>>> >>>> Then, xen/arch/arm/ioreq.c:handle_mmio() gets called by >>>> handle_hvm_io_completion() after QEMU completes the emulation. Today, >>>> handle_mmio just sets the user register with the read value. >>>> >>>> But it would be better if it called again the original function >>>> do_trap_stage2_abort_guest to actually retry the original operation. >>>> This time do_trap_stage2_abort_guest calls try_handle_mmio() and gets >>>> IO_HANDLED instead of IO_RETRY, >>> I may miss some important point, but I failed to see why >>> try_handle_mmio >>> (try_fwd_ioserv) will return IO_HANDLED instead of IO_RETRY at this >>> stage. >>> Or current try_fwd_ioserv() logic needs rework? >> I think you should check the ioreq->state in try_fwd_ioserv(), if the >> result is ready, then ioreq->state should be STATE_IORESP_READY, and you >> can return IO_HANDLED. > I optimized test patch a bit (now it looks much simpler). I didn't face any issues during a quick test. Julien, Stefano, what do you think it does proper things for addressing TODO? Or I missed something? ---  xen/arch/arm/io.c    | 4 ----  xen/arch/arm/ioreq.c | 7 ++++++-  xen/arch/arm/traps.c | 4 +++-  3 files changed, 9 insertions(+), 6 deletions(-) diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c index 436f669..3063577 100644 --- a/xen/arch/arm/io.c +++ b/xen/arch/arm/io.c @@ -156,10 +156,6 @@ static enum io_state try_fwd_ioserv(struct cpu_user_regs *regs,      else          vio->io_completion = HVMIO_mmio_completion; -    /* XXX: Decide what to do */ -    if ( rc == IO_RETRY ) -        rc = IO_HANDLED; -      return rc;  }  #endif diff --git a/xen/arch/arm/ioreq.c b/xen/arch/arm/ioreq.c index 8f60c41..e5235c6 100644 --- a/xen/arch/arm/ioreq.c +++ b/xen/arch/arm/ioreq.c @@ -33,6 +33,8 @@  #include  #include +#include +  bool handle_mmio(void)  {      struct vcpu *v = current; @@ -52,7 +54,7 @@ bool handle_mmio(void)      /* XXX: Do we need to take care of write here ? */      if ( dabt.write ) -        return true; +        goto done;      /*       * Sign extend if required. @@ -72,6 +74,9 @@ bool handle_mmio(void)      set_user_reg(regs, dabt.reg, r); +done: +    advance_pc(regs, hsr); +      return true;  } diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c index ea472d1..974c744 100644 --- a/xen/arch/arm/traps.c +++ b/xen/arch/arm/traps.c @@ -1965,11 +1965,13 @@ static void do_trap_stage2_abort_guest(struct cpu_user_regs *regs,              case IO_HANDLED:                  advance_pc(regs, hsr);                  return; +            case IO_RETRY: +                /* finish later */ +                return;              case IO_UNHANDLED:                  /* IO unhandled, try another way to handle it. */                  break;              default: -                /* XXX: Handle IO_RETRY */                  ASSERT_UNREACHABLE();              }          } -- 2.7.4 -- Regards, Oleksandr Tyshchenko