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Tue, 18 May 2021 15:17:06 +0000 Received: from [54.239.6.187] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1lj1Sz-0008Kf-Ro; Tue, 18 May 2021 15:17:05 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=Jb/nZpPfWCK59tKvpib0PXBBg+ntRrhpI15dC4MYvr8=; b=a/2T2mhtsV++KtKHRMnr0ZIel3 VC587ykPBswkELrePHDn64klODKnwAOZ/fa0TzhgoBFxDUAF1fj8uYV0Z3gnP++U9TROWW0bKelaS QMrNuQXG9lid24qHACZEYRH8R/zUeTsRqXgvqaeDZNMiOkLQ9Lz9/IUQ3uZcRZm137g4=; Subject: Re: [PATCH v3 2/5] xen/common: Guard iommu symbols with CONFIG_HAS_PASSTHROUGH To: Jan Beulich , Connor Davis Cc: Bobby Eshleman , Alistair Francis , Andrew Cooper , George Dunlap , Ian Jackson , Stefano Stabellini , Wei Liu , Paul Durrant , xen-devel@lists.xenproject.org References: <1156cb116da19ef64323e472bb6b6e87c6c73d77.1621017334.git.connojdavis@gmail.com> <556d1933-3b11-0780-edec-b6dc1729bc56@suse.com> <98b429d0-2673-624e-1690-9c0e8373ed5b@xen.org> <7cf966f6-7ccf-ba63-2b67-129577a7ca53@gmail.com> <8e415cac-a8b3-67a6-2f7b-489b964ceb50@suse.com> <922c6304-9299-a697-2405-1b7f6d069842@suse.com> From: Julien Grall Message-ID: Date: Tue, 18 May 2021 16:17:03 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <922c6304-9299-a697-2405-1b7f6d069842@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit Hi Jan, On 18/05/2021 16:13, Jan Beulich wrote: > On 18.05.2021 16:06, Julien Grall wrote: >> >> >> On 18/05/2021 07:27, Jan Beulich wrote: >>> On 18.05.2021 06:11, Connor Davis wrote: >>>> >>>> On 5/17/21 9:42 AM, Julien Grall wrote: >>>>> Hi Jan, >>>>> >>>>> On 17/05/2021 12:16, Jan Beulich wrote: >>>>>> On 14.05.2021 20:53, Connor Davis wrote: >>>>>>> --- a/xen/common/memory.c >>>>>>> +++ b/xen/common/memory.c >>>>>>> @@ -294,7 +294,9 @@ int guest_remove_page(struct domain *d, unsigned >>>>>>> long gmfn) >>>>>>>       p2m_type_t p2mt; >>>>>>>   #endif >>>>>>>       mfn_t mfn; >>>>>>> +#ifdef CONFIG_HAS_PASSTHROUGH >>>>>>>       bool *dont_flush_p, dont_flush; >>>>>>> +#endif >>>>>>>       int rc; >>>>>>>     #ifdef CONFIG_X86 >>>>>>> @@ -385,13 +387,17 @@ int guest_remove_page(struct domain *d, >>>>>>> unsigned long gmfn) >>>>>>>        * Since we're likely to free the page below, we need to suspend >>>>>>>        * xenmem_add_to_physmap()'s suppressing of IOMMU TLB flushes. >>>>>>>        */ >>>>>>> +#ifdef CONFIG_HAS_PASSTHROUGH >>>>>>>       dont_flush_p = &this_cpu(iommu_dont_flush_iotlb); >>>>>>>       dont_flush = *dont_flush_p; >>>>>>>       *dont_flush_p = false; >>>>>>> +#endif >>>>>>>         rc = guest_physmap_remove_page(d, _gfn(gmfn), mfn, 0); >>>>>>>   +#ifdef CONFIG_HAS_PASSTHROUGH >>>>>>>       *dont_flush_p = dont_flush; >>>>>>> +#endif >>>>>>>         /* >>>>>>>        * With the lack of an IOMMU on some platforms, domains with >>>>>>> DMA-capable >>>>>>> @@ -839,11 +845,13 @@ int xenmem_add_to_physmap(struct domain *d, >>>>>>> struct xen_add_to_physmap *xatp, >>>>>>>       xatp->gpfn += start; >>>>>>>       xatp->size -= start; >>>>>>>   +#ifdef CONFIG_HAS_PASSTHROUGH >>>>>>>       if ( is_iommu_enabled(d) ) >>>>>>>       { >>>>>>>          this_cpu(iommu_dont_flush_iotlb) = 1; >>>>>>>          extra.ppage = &pages[0]; >>>>>>>       } >>>>>>> +#endif >>>>>>>         while ( xatp->size > done ) >>>>>>>       { >>>>>>> @@ -868,6 +876,7 @@ int xenmem_add_to_physmap(struct domain *d, >>>>>>> struct xen_add_to_physmap *xatp, >>>>>>>           } >>>>>>>       } >>>>>>>   +#ifdef CONFIG_HAS_PASSTHROUGH >>>>>>>       if ( is_iommu_enabled(d) ) >>>>>>>       { >>>>>>>           int ret; >>>>>>> @@ -894,6 +903,7 @@ int xenmem_add_to_physmap(struct domain *d, >>>>>>> struct xen_add_to_physmap *xatp, >>>>>>>           if ( unlikely(ret) && rc >= 0 ) >>>>>>>               rc = ret; >>>>>>>       } >>>>>>> +#endif >>>>>>>         return rc; >>>>>>>   } >>>>>> >>>>>> I wonder whether all of these wouldn't better become CONFIG_X86: >>>>>> ISTR Julien indicating that he doesn't see the override getting used >>>>>> on Arm. (Julien, please correct me if I'm misremembering.) >>>>> >>>>> Right, so far, I haven't been in favor to introduce it because: >>>>>    1) The P2M code may free some memory. So you can't always ignore >>>>> the flush (I think this is wrong for the upper layer to know when this >>>>> can happen). >>>>>    2) It is unclear what happen if the IOMMU TLBs and the PT contains >>>>> different mappings (I received conflicted advice). >>>>> >>>>> So it is better to always flush and as early as possible. >>>> >>>> So keep it as is or switch to CONFIG_X86? >>> >>> Please switch, unless anyone else voices a strong opinion towards >>> keeping as is. >> >> I would like to avoid adding more #ifdef CONFIG_X86 in the common code. >> Can we instead provide a wrapper for them? > > Doable, sure, but I don't know whether Connor is up to going this > more extensive route. That's a fair point. If that the case, then I prefer the #ifdef CONFIG_HAS_PASSTHROUGH version. I can add an item in my todo list to introduce some helpers. Cheers, -- Julien Grall