[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [future abi] [RFC PATCH V3] xen/gnttab: Store frame GFN in struct page_info on Arm
- To: Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 23 Sep 2021 21:59:26 +0100
- Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none
- Arc-message-signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=16Ef2jl80sOM5zhrzx/z6n+coMQrh2Uz54KD8xBEkPY=; b=eLuzP/VefyjfW4p0g1AG8pCtBZOJxkqLLxgCQKKKNvDtLcv15qR9w5fr9zV5PaWyh/oAwS3+NSi9RcMWhSNnj0E+pFEy8RSLsj8BrrXKmpIVg3de6nEXXUI+UrdXdV0FBLrnUQ7hAgdi77HyNjv3a2sETOnVnkfURcQfJngfNqh1Hcyyb1ztdhGKRq81G7Yo9081+qt9z5M9FFGhteI0lOHvbDga+32dBOCwNgkiGTmrZVxRBQ0sZdO9zFiIqWpBiuHi1Pgl2exs1Wg7uyKU7ksasRBWPH2LHFVCPa2j+WONf/3uou5OlPpHnnzvJ0PMfLkd0OE7SIqFSKuRkZmzww==
- Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=fxQinuiTKGoB4ZGWEWVzXfuQ5XrtakgHAWZiJvox3JZ9/PCRj4tcV5haall2nheFhkqxFS8oyEDCOMAer5pPH7Qp4jrXHqwZ/QwP5z+miE61mmXC7axzViTCm1Es52lBX+KUoDpjuKFKt9V865tmu4TMz6jlQ5BDNkbhHE7oJwN23kDYqUMATxwRyCq4unIqmM0bjt+mc6YVAR0DgnlnH+iUTzSlWeg/d3YuXNifCvJP5GaCyQ94nZfr/BA5hQzmHCemIhqzDD+FOsDiZuotxzLYh//olThRTw2tJUziqEmWnqovu1bUNfaeUvTQWxBnfpSMXf7paByN9OGcJf37SA==
- Authentication-results: esa5.hc3370-68.iphmx.com; dkim=pass (signature verified) header.i=@citrix.onmicrosoft.com
- Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 23 Sep 2021 20:59:45 +0000
- Ironport-data: A9a23:SnN8k64KSKgLovPOyZyUPgxRtFHBchMFZxGqfqrLsTDasY5as4F+v jQaX27UOKzea2fwedskO42/80gE6sOGmIVqSwNorCo2Hi5G8cbLO4+Ufxz6V8+wwmwvb67FA +E2MISowBUcFyeEzvuV3zyIQUBUjclkfJKlYAL/En03FVIMpBsJ00o5wrZo2NUw27BVPivW0 T/Mi5yHULOa82Yc3lI8s8pvfzs24ZweEBtB1rAPTagjUG32zhH5P7pGTU2FFFPqQ5E8IwKPb 72rIIdVXI/u10xF5tuNyt4Xe6CRK1LYFVDmZnF+A8BOjvXez8CbP2lS2Pc0MC9qZzu1c99Z5 8hDtp2CRw0TYYLJhelFWh10A3xZBPgTkFPHCSDXXc27ykTHdz3nwul0DVFwNoodkgp1KTgQr 7pCcmlLN03dwbLtqF64YrAEasALBc/nJo4A/FpnyinUF60OSpHfWaTao9Rf2V/cg+gTRq6OP JpCNlKDajzpRSEIFAwxBKsau8z4qV/1LQZY+FG88P9fD2/7k1UqjemF3MDuUtuOSMZOl0CUv FXa7n/5CREXMt+Y4Ted+3fqjejK9QvgQ54bHrC88v9sgXWQy3YVBRlQUkG0ydG+jkO9QM5OM Ew89S8nrKx0/0uuJvHtUhv9rHOasxo0X9tLD/Z8+AyL0rDT4QuSGi4DVDEpQN47sM47QxQ62 1nPmMnmbRRturCITXOW9p+PsCi/fyMSKAcqeissXQYDpd75r+kbsBXLSdpyFb+vuff8Ezrw3 jOioTA3gvMYistj/6Sk/3jXjjS0vJ/LQwUpoALNUQqYAhhRPdD/IdbysB6CsKgGfN3xokS9U GYstNWQ7+E8A5u3ywOIXehVFbWF96uiCWiJ6bJwJKUJ+zOo8n+lWIlf5jBiOUtkWvo5lS/Vj Fz74lwKucUNVJe+ReouOdvgVphzpUT1PYm9Dpjpgsxyjo+dneNt1BpnY1KZl0vpmVIl+U3UE cbGKZv0ZZr25KIO8dZXewv/+eNwrszd7TmKLXwe8/hB+eDFDJJyYe1ZWGZilshjsMu5TPz9q r6zzfeixRRFS/HZaSLK64MVJl1iBSFlXsqt8JQPLbDZc1sO9IQd5xn5m+hJl2tNxfg9qws11 ivlBh8wJKTX3xUr1jlmmlg8MeiyDP6TXFowPDA2PEbA5pTQSdzH0UvrTLNuJeNP3LU6lZZcF qBZE+3dUqUnYmmWoFw1MMiixLGOgTz23GpiyQL+O2NhF3OhLiSUkuLZkvzHrnJTUXbn6ZVk8 9VNFGrzGPI+euirN+6PANqHxFKtp3kN3uV0WkrDON5If0vwtoNtLkTMYjUfeqng8D3PmWmX0 Ri4GxAdqbWfqoM56oCR16uFs52oA611GU8DRzvX6rO/NC/7+Gu/wNAfDLbULG6FDG6kqr+/Y eh1zu3nNKFVllh9rIchQa1gyrgz5oWzquYCnBhkBnjCc3+iFqhkfiudxcBKu6AUnu1ZtAK6V 1ih4N5fPbnVasrpHERIfFgub/iZ1OFSkT7XtKxnLEL/7S5x3byGTUQNYEXc1H0DdON4adp3z /0gtcga7x2EpiAratvW3DpJ82msL2AbV/l1vJ8tH4K22BEgzUtPYMKAB3auso2PcdhFLmIjP iSQ2PjZn71Zy0fPLygzGHzK0bYPjJgCokkXnloLJlDPkdvZnP4nmhZW9G1vHAhSyxxG1cN1O 3RqaBIpdfnfoW8wiZgRRX2oFiFAGAadqx74xFY+nWHES1WlCz7WJ2onNOfRpE0U/gqwpNSAE G10HIo9bQvXQQ==
- Ironport-hdrordr: A9a23:BMWM6KwUqstIo8Q4VABeKrPxu+skLtp133Aq2lEZdPULSKOlfp GV8MjziyWYtN9wYhAdcdDpAtjkfZquz+8L3WB3B8bfYOCGghrUEGgG1+XfKlLbalXDH4JmpM Bdmu1FeafN5DtB/LbHCWuDYq8dKbC8mcjC74eurAYfcegpUdAF0+4QMHfrLqQcfnghOXNWLu v/2iMKnUvaRZxBBf7LeEXtEtKz6+HjpdbDW1orFhQn4A6BgXeB76P7KQGR2lM7XylUybkv3G DZm0ihj5/T/c2T+1v57Sv+/p5WkNzuxp9qA9GNsNEcLnHJhhyzbIpsdrWetHQeof2p6nwtjN 7Qyi1QcPhb2jf0RCWYsBHt0w7v3HIH7GLj80aRhT/ZrcnwVFsBeoF8rLMcViGcx1srvdl63q 4O9XmerYBrARTJmzm4z8TUVjlx/3DE4kYKoKo2tThyQIEeYLheocg050VOCqoNGyr89cQODP RuNsfB//xbGGnqL0wxhlMfheBEY05DWitvGiM5y4uoOnlt7TFEJnIjtY4idixqzuN6d3FGj9 60epiA2os+F/P/wMpGdZA8qPCMexnwqCT3QSuvyGTcZdM60k322urKCZUOlauXkc8zvdYPcK qoaiIviYd1QTO3NfGz
- Ironport-sdr: kfEWHmL5/7mwAxt12gGwBwI3BWL3ne4EBCOHBmVHObFZ5poTg+MdfrY6Y+uSbThsPVcLXJxGAd 6gJezyA5+3rwlvg590IXI6JiDUdw5hBLX78x9hvcu8cgYg8cjU4uuGHzlKxDLMmuP+pEn/mAl7 AZiQ0P2/hq41913btySXFwvcGHFoUMUcSBM2wrRrKuomSDx5q40PlFg2JnMQ303aZ0lw0wPlv4 Pi9smCM4UWeFOfoAPUEPSDDUJbOFooY91TUNAkjX9w5iKqtlQoSHXyG4z43BryPea6DjW6fEra 08vKLa7QyaUbMSr41wKbLHsY
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 23/09/2021 20:32, Oleksandr Tyshchenko wrote:
> Suggested-by: Julien Grall <jgrall@xxxxxxxxxx>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> ---
> You can find the related discussions at:
> https://lore.kernel.org/xen-devel/93d0df14-2c8a-c2e3-8c51-54412190171c@xxxxxxx/
> https://lore.kernel.org/xen-devel/1628890077-12545-1-git-send-email-olekstysh@xxxxxxxxx/
> https://lore.kernel.org/xen-devel/1631652245-30746-1-git-send-email-olekstysh@xxxxxxxxx/
>
> ! Please note, there is still unresolved locking question here for which
> I failed to find a suitable solution. So, it is still an RFC !
Just FYI, I thought I'd share some of the plans for ABI v2. Obviously
these plans are future work and don't solve the current problem.
Guests mapping Xen pages is backwards. There are reasons why it was
used for x86 PV guests, but the entire interface should have been design
differently for x86 HVM.
In particular, Xen should be mapping guest RAM, rather than the guest
manipulating the 2nd stage tables to map Xen RAM. Amongst other things,
its far far lower overhead.
A much better design is one where the grant table looks like an MMIO
device. The domain builder decides the ABI (v1 vs v2 - none of this
dynamic switch at runtime nonsense), and picks a block of guest physical
addresses, which are registered with Xen. This forms the grant table,
status table (v2 only), and holes to map into. Details can be conveyed
via ACPI table or DT, as applicable
Xen maps the RAM (which is now accounted to the guest, an improvement
over today) forming the grant and status tables, and grant map/unmap
hypercalls simplify massively to just {src domid, gref, flags} => slot,
which also solves the "is the same grant mapped elsewhere?" problem.
There is never a need for HVM guests to map the same grant twice (as it
controls the first stage tables and can create whatever alias it
desires), but there's also no need to allow the guest to pick where the
mapping occurs. This vastly simplifies both the Xen and guest kernel
implementations.
~Andrew
|
