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Re: [Xen-devel] L1TF, and future work
- To: Jason Andryuk <jandryuk@xxxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Sat, 25 Aug 2018 07:21:33 +0200
- Autocrypt: addr=jgross@xxxxxxxx; prefer-encrypt=mutual; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNHkp1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmRlPsLAeQQTAQIAIwUCU4xw6wIbAwcL CQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJELDendYovxMvi4UH/Ri+OXlObzqMANruTd4N zmVBAZgx1VW6jLc8JZjQuJPSsd/a+bNr3BZeLV6lu4Pf1Yl2Log129EX1KWYiFFvPbIiq5M5 kOXTO8Eas4CaScCvAZ9jCMQCgK3pFqYgirwTgfwnPtxFxO/F3ZcS8jovza5khkSKL9JGq8Nk czDTruQ/oy0WUHdUr9uwEfiD9yPFOGqp4S6cISuzBMvaAiC5YGdUGXuPZKXLpnGSjkZswUzY d9BVSitRL5ldsQCg6GhDoEAeIhUC4SQnT9SOWkoDOSFRXZ+7+WIBGLiWMd+yKDdRG5RyP/8f 3tgGiB6cyuYfPDRGsELGjUaTUq3H2xZgIPfOwE0EU4xwFgEIAMsx+gDjgzAY4H1hPVXgoLK8 B93sTQFN9oC6tsb46VpxyLPfJ3T1A6Z6MVkLoCejKTJ3K9MUsBZhxIJ0hIyvzwI6aYJsnOew cCiCN7FeKJ/oA1RSUemPGUcIJwQuZlTOiY0OcQ5PFkV5YxMUX1F/aTYXROXgTmSaw0aC1Jpo w7Ss1mg4SIP/tR88/d1+HwkJDVW1RSxC1PWzGizwRv8eauImGdpNnseneO2BNWRXTJumAWDD pYxpGSsGHXuZXTPZqOOZpsHtInFyi5KRHSFyk2Xigzvh3b9WqhbgHHHE4PUVw0I5sIQt8hJq 5nH5dPqz4ITtCL9zjiJsExHuHKN3NZsAEQEAAcLAXwQYAQIACQUCU4xwFgIbDAAKCRCw3p3W KL8TL0P4B/9YWver5uD/y/m0KScK2f3Z3mXJhME23vGBbMNlfwbr+meDMrJZ950CuWWnQ+d+ Ahe0w1X7e3wuLVODzjcReQ/v7b4JD3wwHxe+88tgB9byc0NXzlPJWBaWV01yB2/uefVKryAf AHYEd0gCRhx7eESgNBe3+YqWAQawunMlycsqKa09dBDL1PFRosF708ic9346GLHRc6Vj5SRA UTHnQqLetIOXZm3a2eQ1gpQK9MmruO86Vo93p39bS1mqnLLspVrL4rhoyhsOyh0Hd28QCzpJ wKeHTd0MAWAirmewHXWPco8p1Wg+V+5xfZzuQY0f4tQxvOpXpt4gQ1817GQ5/Ed/wsDtBBgB CAAgFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAlrd8NACGwIAgQkQsN6d1ii/Ey92IAQZFggA HRYhBFMtsHpB9jjzHji4HoBcYbtP2GO+BQJa3fDQAAoJEIBcYbtP2GO+TYsA/30H/0V6cr/W V+J/FCayg6uNtm3MJLo4rE+o4sdpjjsGAQCooqffpgA+luTT13YZNV62hAnCLKXH9n3+ZAgJ RtAyDWk1B/0SMDVs1wxufMkKC3Q/1D3BYIvBlrTVKdBYXPxngcRoqV2J77lscEvkLNUGsu/z W2pf7+P3mWWlrPMJdlbax00vevyBeqtqNKjHstHatgMZ2W0CFC4hJ3YEetuRBURYPiGzuJXU pAd7a7BdsqWC4o+GTm5tnGrCyD+4gfDSpkOT53S/GNO07YkPkm/8J4OBoFfgSaCnQ1izwgJQ jIpcG2fPCI2/hxf2oqXPYbKr1v4Z1wthmoyUgGN0LPTIm+B5vdY82wI5qe9uN6UOGyTH2B3p hRQUWqCwu2sqkI3LLbTdrnyDZaixT2T0f4tyF5Lfs+Ha8xVMhIyzNb1byDI5FKCb
- Cc: sergey.dyasli@xxxxxxxxxx, Wei Liu <wei.liu2@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, tim@xxxxxxx, xen-devel@xxxxxxxxxxxxx, Jan Beulich <JBeulich@xxxxxxxx>, security@xxxxxxx, dfaggioli@xxxxxxxx, dwmw@xxxxxxxxxxxx, roger.pau@xxxxxxxxxx
- Delivery-date: Sat, 25 Aug 2018 05:21:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 24/08/18 20:43, Jason Andryuk wrote:
> On Wed, Aug 15, 2018 at 10:39 AM Juergen Gross <jgross@xxxxxxxx> wrote:
>>
>> On 15/08/18 16:10, Jan Beulich wrote:
>>>>>> On 15.08.18 at 15:17, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> 2) 32bit PV guests which use writeable pagetable support will
>>>> automatically get shadowed when the clear the lower half.
>>>
>>> ... of a page table entry.
>>>
>>>> Ideally, such
>>>> guests should be modified to use hypercalls rather than the ptwr
>>>> infrastructure (as its more efficient to begin with), but we can
>>>> probably work around this in Xen by emulating the next few instructions
>>>> until we have a complete PTE (same as the shadow code).
>>>
>>> Provided the intervening insns are simple enough. I've looked into
>>> current Linux pv-ops code the other day, and afaict it's already
>>> using mmu-op or cmpxchg8b, but not two separate mov-s. But
>>> of course I've looked at the general routines only, not at things
>>> perhaps hidden in special cases, or in init-only code.
>>
>> Look at xen_pte_clear(). Inside irq handling it will use (PAE case):
>>
>> static inline void native_pte_clear(struct mm_struct *mm, unsigned long
>> addr,
>> pte_t *ptep)
>> {
>> ptep->pte_low = 0;
>> smp_wmb();
>> ptep->pte_high = 0;
>> }
>
> I've been testing out set_64bit for PTE operations on 32bit PAE. I
> haven't found all the spots, but shadowing is now enabled a few
> seconds into boot instead of immediately.
>
> And yes, I think https://bugzilla.kernel.org/show_bug.cgi?id=198497 is
> related as you presumed a while back.
I have a patch series (two patches) avoiding shadowing completely:
https://lists.xen.org/archives/html/xen-devel/2018-08/msg01785.html
Juergen
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