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(int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 97D9F801E66; Tue, 24 Dec 2019 00:20:41 +0000 (UTC) Received: from [10.18.17.164] (dhcp-17-164.bos.redhat.com [10.18.17.164]) by smtp.corp.redhat.com (Postfix) with ESMTP id F2A095DA60; Tue, 24 Dec 2019 00:20:34 +0000 (UTC) Subject: Re: [PATCH v2 2/2] ide: Fix incorrect handling of some PRDTs in ide_dma_cb() To: Kevin Wolf , Alexander Popov References: <20191216181405.462292-1-alex.popov@linux.com> <20191216181405.462292-2-alex.popov@linux.com> <20191219150136.GL5230@linux.fritz.box> From: John Snow Autocrypt: addr=jsnow@redhat.com; prefer-encrypt=mutual; keydata= mQINBFTKefwBEAChvwqYC6saTzawbih87LqBYq0d5A8jXYXaiFMV/EvMSDqqY4EY6whXliNO IYzhgrPEe7ZmPxbCSe4iMykjhwMh5byIHDoPGDU+FsQty2KXuoxto+ZdrP9gymAgmyqdk3aV vzzmCa3cOppcqKvA0Kqr10UeX/z4OMVV390V+DVWUvzXpda45/Sxup57pk+hyY52wxxjIqef 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List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrea Arcangeli , Laurent Vivier , Darren Kenny , sstabellini@kernel.org, pmatouse@redhat.com, mdroth@linux.vnet.ibm.com, qemu-block@nongnu.org, "Michael S . Tsirkin" , qemu-stable@nongnu.org, qemu-devel@nongnu.org, Kashyap Chamarthy , Thomas Huth , Paolo Bonzini , pjp@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 12/19/19 10:01 AM, Kevin Wolf wrote: > Am 16.12.2019 um 19:14 hat Alexander Popov geschrieben: >> The commit a718978ed58a from July 2015 introduced the assertion which >> implies that the size of successful DMA transfers handled in ide_dma_cb() >> should be multiple of 512 (the size of a sector). But guest systems can >> initiate DMA transfers that don't fit this requirement. >> >> For fixing that let's check the number of bytes prepared for the transfer >> by the prepare_buf() handler. The code in ide_dma_cb() must behave >> according to the Programming Interface for Bus Master IDE Controller >> (Revision 1.0 5/16/94): >> 1. If PRDs specified a smaller size than the IDE transfer >> size, then the Interrupt and Active bits in the Controller >> status register are not set (Error Condition). >> 2. If the size of the physical memory regions was equal to >> the IDE device transfer size, the Interrupt bit in the >> Controller status register is set to 1, Active bit is set to 0. >> 3. If PRDs specified a larger size than the IDE transfer size, >> the Interrupt and Active bits in the Controller status register >> are both set to 1. >> >> Signed-off-by: Alexander Popov >> --- >> hw/ide/core.c | 30 ++++++++++++++++++++++-------- >> 1 file changed, 22 insertions(+), 8 deletions(-) >> >> diff --git a/hw/ide/core.c b/hw/ide/core.c >> index 754ff4dc34..171831c7bd 100644 >> --- a/hw/ide/core.c >> +++ b/hw/ide/core.c >> @@ -849,6 +849,7 @@ static void ide_dma_cb(void *opaque, int ret) >> int64_t sector_num; >> uint64_t offset; >> bool stay_active = false; >> + int32_t prep_size = 0; >> >> if (ret == -EINVAL) { >> ide_dma_error(s); >> @@ -863,13 +864,15 @@ static void ide_dma_cb(void *opaque, int ret) >> } >> } >> >> - n = s->io_buffer_size >> 9; >> - if (n > s->nsector) { >> - /* The PRDs were longer than needed for this request. Shorten them so >> - * we don't get a negative remainder. The Active bit must remain set >> - * after the request completes. */ >> + if (s->io_buffer_size > s->nsector * 512) { >> + /* >> + * The PRDs were longer than needed for this request. >> + * The Active bit must remain set after the request completes. >> + */ >> n = s->nsector; >> stay_active = true; >> + } else { >> + n = s->io_buffer_size >> 9; >> } >> >> sector_num = ide_get_sector(s); >> @@ -892,9 +895,20 @@ static void ide_dma_cb(void *opaque, int ret) >> n = s->nsector; >> s->io_buffer_index = 0; >> s->io_buffer_size = n * 512; >> - if (s->bus->dma->ops->prepare_buf(s->bus->dma, s->io_buffer_size) < 512) { >> - /* The PRDs were too short. Reset the Active bit, but don't raise an >> - * interrupt. */ >> + prep_size = s->bus->dma->ops->prepare_buf(s->bus->dma, s->io_buffer_size); >> + /* prepare_buf() must succeed and respect the limit */ >> + assert(prep_size > 0 && prep_size <= n * 512); > > Hm, I'm not sure about prep_size > 0. Maybe it's true for > bmdma_prepare_buf() for PCI (I'm not even sure there: What happens if we > pass a PRDT with 0 entries? Should we have another test case for this?), > but other controllers like AHCI don't seem to interpret an entry with > size 0 as maximum size. > > John, what do you think? > I've been out to lunch for a little while. There are some issues that I recall with IDE, but couldn't find the time to fix prior to 4.2. I'll review all the outstanding IDE problems I am aware of and review these series before the end of the year. >> + /* >> + * Now prep_size stores the number of bytes in the sglist, and >> + * s->io_buffer_size stores the number of bytes described by the PRDs. >> + */ >> + >> + if (prep_size < n * 512) { >> + /* >> + * The PRDs are too short for this request. Error condition! >> + * Reset the Active bit and don't raise the interrupt. >> + */ >> s->status = READY_STAT | SEEK_STAT; >> dma_buf_commit(s, 0); >> goto eot; > > Here you decided that we don't need to do partial I/O for short PRDTs. I > think my conclusion was that the spec doesn't really say what we need to > do, so this is fine with me. > > Apart from the assertion above, the patch looks good to me. > > Kevin >