From: Auger Eric <eric.auger@redhat.com> To: Alexey Kardashevskiy <aik@ozlabs.ru>, Alex Williamson <alex.williamson@redhat.com> Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org Subject: Re: [RFC PATCH] vfio/pci: Add ioeventfd support Date: Tue, 13 Mar 2018 13:38:00 +0100 [thread overview] Message-ID: <777482c6-8180-df0f-0a0c-5d6e000553ba@redhat.com> (raw) In-Reply-To: <86c09adf-c4ab-5eca-629a-4d6c6a5692be@ozlabs.ru> Hi, On 08/02/18 02:22, Alexey Kardashevskiy wrote: > On 08/02/18 01:12, Alex Williamson wrote: >> On Wed, 7 Feb 2018 15:48:26 +1100 >> Alexey Kardashevskiy <aik@ozlabs.ru> wrote: >> >>> On 07/02/18 15:25, Alex Williamson wrote: >>>> On Wed, 7 Feb 2018 15:09:22 +1100 >>>> Alexey Kardashevskiy <aik@ozlabs.ru> wrote: >>>>> On 07/02/18 11:08, Alex Williamson wrote: >>>>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h >>>>>> index e3301dbd27d4..07966a5f0832 100644 >>>>>> --- a/include/uapi/linux/vfio.h >>>>>> +++ b/include/uapi/linux/vfio.h >>>>>> @@ -503,6 +503,30 @@ struct vfio_pci_hot_reset { >>>>>> >>>>>> #define VFIO_DEVICE_PCI_HOT_RESET _IO(VFIO_TYPE, VFIO_BASE + 13) >>>>>> >>>>>> +/** >>>>>> + * VFIO_DEVICE_IOEVENTFD - _IOW(VFIO_TYPE, VFIO_BASE + 14, >>>>>> + * struct vfio_device_ioeventfd) >>>>>> + * >>>>>> + * Perform a write to the device at the specified device fd offset, with >>>>>> + * the specified data and width when the provided eventfd is triggered. >>>>>> + * >>>>>> + * Return: 0 on success, -errno on failure. >>>>>> + */ >>>>>> +struct vfio_device_ioeventfd { >>>>>> + __u32 argsz; >>>>>> + __u32 flags; >>>>>> +#define VFIO_DEVICE_IOEVENTFD_8 (1 << 0) /* 1-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_16 (1 << 1) /* 2-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_32 (1 << 2) /* 4-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_64 (1 << 3) /* 8-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_SIZE_MASK (0xf) >>>>>> + __u64 offset; /* device fd offset of write */ >>>>>> + __u64 data; /* data to be written */ >>>>>> + __s32 fd; /* -1 for de-assignment */ >>>>>> +}; >>>>>> + >>>>>> +#define VFIO_DEVICE_IOEVENTFD _IO(VFIO_TYPE, VFIO_BASE + 14) >>>>> >>>>> >>>>> Is this a first ioctl with endianness fixed to little-endian? I'd suggest >>>>> to comment on that as things like vfio_info_cap_header do use the host >>>>> endianness. >>>> >>>> Look at our current read and write interface, we call leXX_to_cpu >>>> before calling iowriteXX there and I think a user would logically >>>> expect to use the same data format here as they would there. >>> >>> If the data is "char data[8]" (i.e. bytestream), then it can be expected to >>> be device/bus endian (i.e. PCI == little endian), but if it is u64 - then I >>> am not so sure really, and this made me look around. It could be "__le64 >>> data" too. >>> >>>> Also note >>>> that iowriteXX does a cpu_to_leXX, so are we really defining the >>>> interface as little-endian or are we just trying to make ourselves >>>> endian neutral and counter that implicit conversion? Thanks, >>> >>> Defining it LE is fine, I just find it a bit confusing when >>> vfio_info_cap_header is host endian but vfio_device_ioeventfd is not. >> >> But I don't think we are defining the interface as little-endian. >> iowriteXX does a cpu_to_leXX byteswap. Therefore in order to maintain >> endian neutrality, if the data does a cpu->le swap on the way out, I >> need to do a le->cpu swap on the way in, right? Please defend the >> assertion that we're creating a little-endian interface. Thanks, > > > vfio_pci_ioctl() passes "endian-neutral" ioeventfd.data to > vfio_pci_ioeventfd() which immediately does the leXX_to_cpu() conversion > (and uses the result later on in iowriteXX(), which is not VFIO API) so I > read it as the ioctl really expects LE. > > The QEMU part - vfio_nvidia_mirror_quirk MR - does not swap bytes but the > MR itself it declared DEVICE_LITTLE_ENDIAN which means > vfio_nvidia_quirk_mirror_write() receives byteswapped @data in the host > endian == bigendian on a big endian host. So the ioctl() handler will > receive a BE value, do byteswap #1 in leXX_to_cpu(), and then do byteswap > #2 in iowriteXX() so after all a BE will be written to a device. So I'd say > we rather do not need leXX_to_cpu() in vfio_pci_ioeventfd(). Correct me > where I am wrong. Thanks, It is not crystal clear to me what is the outcome of this discussion. Please can you clarify? At the beginning I understood we had a chain of lexx_to_cpu and cpu_to_lexx (in iowritexx) so it was neutral. Now I am lost about what we want. Thanks Eric > > >
WARNING: multiple messages have this Message-ID (diff)
From: Auger Eric <eric.auger@redhat.com> To: Alexey Kardashevskiy <aik@ozlabs.ru>, Alex Williamson <alex.williamson@redhat.com> Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org Subject: Re: [Qemu-devel] [RFC PATCH] vfio/pci: Add ioeventfd support Date: Tue, 13 Mar 2018 13:38:00 +0100 [thread overview] Message-ID: <777482c6-8180-df0f-0a0c-5d6e000553ba@redhat.com> (raw) In-Reply-To: <86c09adf-c4ab-5eca-629a-4d6c6a5692be@ozlabs.ru> Hi, On 08/02/18 02:22, Alexey Kardashevskiy wrote: > On 08/02/18 01:12, Alex Williamson wrote: >> On Wed, 7 Feb 2018 15:48:26 +1100 >> Alexey Kardashevskiy <aik@ozlabs.ru> wrote: >> >>> On 07/02/18 15:25, Alex Williamson wrote: >>>> On Wed, 7 Feb 2018 15:09:22 +1100 >>>> Alexey Kardashevskiy <aik@ozlabs.ru> wrote: >>>>> On 07/02/18 11:08, Alex Williamson wrote: >>>>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h >>>>>> index e3301dbd27d4..07966a5f0832 100644 >>>>>> --- a/include/uapi/linux/vfio.h >>>>>> +++ b/include/uapi/linux/vfio.h >>>>>> @@ -503,6 +503,30 @@ struct vfio_pci_hot_reset { >>>>>> >>>>>> #define VFIO_DEVICE_PCI_HOT_RESET _IO(VFIO_TYPE, VFIO_BASE + 13) >>>>>> >>>>>> +/** >>>>>> + * VFIO_DEVICE_IOEVENTFD - _IOW(VFIO_TYPE, VFIO_BASE + 14, >>>>>> + * struct vfio_device_ioeventfd) >>>>>> + * >>>>>> + * Perform a write to the device at the specified device fd offset, with >>>>>> + * the specified data and width when the provided eventfd is triggered. >>>>>> + * >>>>>> + * Return: 0 on success, -errno on failure. >>>>>> + */ >>>>>> +struct vfio_device_ioeventfd { >>>>>> + __u32 argsz; >>>>>> + __u32 flags; >>>>>> +#define VFIO_DEVICE_IOEVENTFD_8 (1 << 0) /* 1-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_16 (1 << 1) /* 2-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_32 (1 << 2) /* 4-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_64 (1 << 3) /* 8-byte write */ >>>>>> +#define VFIO_DEVICE_IOEVENTFD_SIZE_MASK (0xf) >>>>>> + __u64 offset; /* device fd offset of write */ >>>>>> + __u64 data; /* data to be written */ >>>>>> + __s32 fd; /* -1 for de-assignment */ >>>>>> +}; >>>>>> + >>>>>> +#define VFIO_DEVICE_IOEVENTFD _IO(VFIO_TYPE, VFIO_BASE + 14) >>>>> >>>>> >>>>> Is this a first ioctl with endianness fixed to little-endian? I'd suggest >>>>> to comment on that as things like vfio_info_cap_header do use the host >>>>> endianness. >>>> >>>> Look at our current read and write interface, we call leXX_to_cpu >>>> before calling iowriteXX there and I think a user would logically >>>> expect to use the same data format here as they would there. >>> >>> If the data is "char data[8]" (i.e. bytestream), then it can be expected to >>> be device/bus endian (i.e. PCI == little endian), but if it is u64 - then I >>> am not so sure really, and this made me look around. It could be "__le64 >>> data" too. >>> >>>> Also note >>>> that iowriteXX does a cpu_to_leXX, so are we really defining the >>>> interface as little-endian or are we just trying to make ourselves >>>> endian neutral and counter that implicit conversion? Thanks, >>> >>> Defining it LE is fine, I just find it a bit confusing when >>> vfio_info_cap_header is host endian but vfio_device_ioeventfd is not. >> >> But I don't think we are defining the interface as little-endian. >> iowriteXX does a cpu_to_leXX byteswap. Therefore in order to maintain >> endian neutrality, if the data does a cpu->le swap on the way out, I >> need to do a le->cpu swap on the way in, right? Please defend the >> assertion that we're creating a little-endian interface. Thanks, > > > vfio_pci_ioctl() passes "endian-neutral" ioeventfd.data to > vfio_pci_ioeventfd() which immediately does the leXX_to_cpu() conversion > (and uses the result later on in iowriteXX(), which is not VFIO API) so I > read it as the ioctl really expects LE. > > The QEMU part - vfio_nvidia_mirror_quirk MR - does not swap bytes but the > MR itself it declared DEVICE_LITTLE_ENDIAN which means > vfio_nvidia_quirk_mirror_write() receives byteswapped @data in the host > endian == bigendian on a big endian host. So the ioctl() handler will > receive a BE value, do byteswap #1 in leXX_to_cpu(), and then do byteswap > #2 in iowriteXX() so after all a BE will be written to a device. So I'd say > we rather do not need leXX_to_cpu() in vfio_pci_ioeventfd(). Correct me > where I am wrong. Thanks, It is not crystal clear to me what is the outcome of this discussion. Please can you clarify? At the beginning I understood we had a chain of lexx_to_cpu and cpu_to_lexx (in iowritexx) so it was neutral. Now I am lost about what we want. Thanks Eric > > >
next prev parent reply other threads:[~2018-03-13 12:38 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-02-07 0:08 [RFC PATCH] vfio/pci: Add ioeventfd support Alex Williamson 2018-02-07 0:08 ` [Qemu-devel] " Alex Williamson 2018-02-07 4:09 ` Alexey Kardashevskiy 2018-02-07 4:09 ` [Qemu-devel] " Alexey Kardashevskiy 2018-02-07 4:25 ` Alex Williamson 2018-02-07 4:25 ` [Qemu-devel] " Alex Williamson 2018-02-07 4:48 ` Alexey Kardashevskiy 2018-02-07 4:48 ` [Qemu-devel] " Alexey Kardashevskiy 2018-02-07 14:12 ` Alex Williamson 2018-02-07 14:12 ` [Qemu-devel] " Alex Williamson 2018-02-08 1:22 ` Alexey Kardashevskiy 2018-02-08 1:22 ` [Qemu-devel] " Alexey Kardashevskiy 2018-03-13 12:38 ` Auger Eric [this message] 2018-03-13 12:38 ` Auger Eric 2018-03-15 21:23 ` Alex Williamson 2018-03-15 21:23 ` [Qemu-devel] " Alex Williamson 2018-02-07 15:46 ` Auger Eric 2018-02-07 16:57 ` Alex Williamson 2018-02-08 13:48 ` Auger Eric 2018-02-09 7:05 ` Peter Xu 2018-02-09 21:45 ` Alex Williamson 2018-02-11 3:09 ` Peter Xu
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