From: Joerg Roedel <jroedel@suse.de>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu/amd: Do not re-fetch iommu->cmd_buf_tail
Date: Wed, 30 Oct 2019 10:20:14 +0100 [thread overview]
Message-ID: <20191030092014.GO838@suse.de> (raw)
In-Reply-To: <20191024125410.19224-1-dvlasenk@redhat.com>
On Thu, Oct 24, 2019 at 02:54:10PM +0200, Denys Vlasenko wrote:
> The compiler is not smart enough to realize that iommu->cmd_buf_tail
> can't be modified across memcpy:
>
> 41 8b 45 74 mov 0x74(%r13),%eax # iommu->cmd_buf_tail
> 44 8d 78 10 lea 0x10(%rax),%r15d # += sizeof(*cmd)
> 41 81 e7 ff 1f 00 00 and $0x1fff,%r15d # %= CMD_BUFFER_SIZE
> 49 03 45 68 add 0x68(%r13),%rax # target = iommu->cmd_buf + iommu->cmd_buf_tail
> 45 89 7d 74 mov %r15d,0x74(%r13) # store to iommu->cmd_buf_tail
> 49 8b 34 24 mov (%r12),%rsi # memcpy
> 49 8b 7c 24 08 mov 0x8(%r12),%rdi # memcpy
> 48 89 30 mov %rsi,(%rax) # memcpy
> 48 89 78 08 mov %rdi,0x8(%rax) # memcpy
> 49 8b 55 38 mov 0x38(%r13),%rdx # iommu->mmio_base
> 41 8b 45 74 mov 0x74(%r13),%eax # redundant load of iommu->cmd_buf_tail
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 89 82 08 20 00 00 mov %eax,0x2008(%rdx) # writel
>
> CC: Tom Lendacky <thomas.lendacky@amd.com>
> CC: Joerg Roedel <jroedel@suse.de>
> CC: linux-kernel@vger.kernel.org
> Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
> ---
> drivers/iommu/amd_iommu.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
Applied, thanks.
prev parent reply other threads:[~2019-10-30 9:20 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-24 12:54 [PATCH] iommu/amd: Do not re-fetch iommu->cmd_buf_tail Denys Vlasenko
2019-10-30 9:20 ` Joerg Roedel [this message]
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