<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:굴림;
panose-1:2 11 6 0 0 1 1 1 1 1;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:"맑은 고딕";
panose-1:2 11 5 3 2 0 0 2 0 4;}
@font-face
{font-family:"\@맑은 고딕";
panose-1:2 11 5 3 2 0 0 2 0 4;}
@font-face
{font-family:"\@굴림";
panose-1:2 11 6 0 0 1 1 1 1 1;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:굴림;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p.msonormal0, li.msonormal0, div.msonormal0
{mso-style-name:msonormal;
mso-margin-top-alt:auto;
margin-right:0cm;
mso-margin-bottom-alt:auto;
margin-left:0cm;
font-size:12.0pt;
font-family:굴림;}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:"맑은 고딕";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"맑은 고딕";}
@page WordSection1
{size:612.0pt 792.0pt;
margin:3.0cm 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=KO link=blue vlink=purple><div class=WordSection1><p class=MsoNormal style='word-break:break-hangul'><span lang=EN-US style='font-size:10.0pt;font-family:"맑은 고딕"'>I see, Thanks a lot! I remember having read about SR-IOV long time ago.<o:p></o:p></span></p><p class=MsoNormal style='word-break:break-hangul'><span lang=EN-US style='font-size:10.0pt;font-family:"맑은 고딕"'>Regards,<o:p></o:p></span></p><p class=MsoNormal style='word-break:break-hangul'><span lang=EN-US style='font-size:10.0pt;font-family:"맑은 고딕"'>Chan Kim<o:p></o:p></span></p><p class=MsoNormal style='word-break:break-hangul'><span lang=EN-US style='font-size:10.0pt;font-family:"맑은 고딕"'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> FMDF <fmdefrancesco@gmail.com> <br><b>Sent:</b> Friday, October 1, 2021 8:41 AM<br><b>To:</b> ckim@etri.re.kr<br><b>Cc:</b> kernelnewbies <kernelnewbies@kernelnewbies.org><br><b>Subject:</b> Re: Can register addresses conversion go through iommu too? probably not..<o:p></o:p></span></p></div></div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><div><div><div><div><p class=MsoNormal><span lang=EN-US>On Thu, 30 Sep 2021, 08:54 , <<a href="mailto:ckim@etri.re.kr">ckim@etri.re.kr</a>> wrote:<o:p></o:p></span></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>[If] the OS is running in virtualized environment (a hypervisor under it), this kernel virtual address should go under conversion twice <o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>1. virtual to physical by OS (this physical is not actually physical, an intermediate physical?)<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>2. intermediate physical to real physical<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>I thought these two conversions are done by kernel or hypervisor software because iommu is for address translation for the addresses that the device </span>“<span lang=EN-US>uses(or generates)</span>”<span lang=EN-US>, not for the kernel to access the device itself. <o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>Is my understanding correct?<o:p></o:p></span></p></div></div></blockquote></div></div><div><p class=MsoNormal><span lang=EN-US>Something similar to what you describe happens with old/deprecated technologies. For example, with Full virtualization I/O operations need to go through two software layers.<o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US style='border:none windowtext 1.0pt;padding:0cm'>Virtual Function I/O</span><span lang=EN-US> (VFIO) exposes direct device access to user space in a secure memory (IOMMU) protected environment. With VFIO, a VM Guest can directly access hardware devices on the VM Host Server. This technique improves performance, if compared both to Full virtualization and Paravirtualization. However, with VFIO, devices cannot be shared with multiple VM guests. <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>Single Root I/O Virtualization (SR-IOV) combines the benefits of performance gains of VFIO and the ability to share a device with several VM Guests (but it requires special hardware that must be capable to appear to two or more VM guests as different devices. <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>Regards, <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>Fabio M. De Francesco<o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>P.S.: For further information about Linux virtualization capabilities, please read <a href="https://en.wikipedia.org/wiki/Linux_kernel#Architecture_and_features">https://en.wikipedia.org/wiki/Linux_kernel#Architecture_and_features</a>.<o:p></o:p></span></p></div><div><div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>Any help will be appreciated.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>Thank you!<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>Chan Kim<o:p></o:p></span></p></div></div></blockquote></div></div></div></div></div></body></html>