From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefano.stabellini@eu.citrix.com (Stefano Stabellini) Date: Thu, 26 Nov 2015 16:04:56 +0000 Subject: [PATCH v3 38/62] arm/acpi: Add placeholder for efi and acpi load address In-Reply-To: <564C6763.6050107@citrix.com> References: <1447753261-7552-1-git-send-email-shannon.zhao@linaro.org> <1447753261-7552-39-git-send-email-shannon.zhao@linaro.org> <564B1666.4060008@citrix.com> <564B2152.9000904@huawei.com> <564B3845.4060801@citrix.com> <564BEA22.1040909@huawei.com> <564C6763.6050107@citrix.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, 18 Nov 2015, Julien Grall wrote: > On 18/11/15 03:01, Shannon Zhao wrote: > > "All above tables will be mapped to Dom0 non-RAM space. Since when > > booting through ACPI it doesn't need the grant table region(see below > > section 3), it could use this region to store the tables or use the same > > way to find one memory region to store them." > > > > Firstly, as Jan suggested, these tables should not be in RAM space, so > > we drop the previous way that copying these tables to Dom0 RAM. > > Then I suggested map these tables to the space after the Dom0 RAM space, > > but this not right because Dom0 RAM region might be at the edge of > > physical RAM space and there might be device MMIO regions. > > Then you suggest it could map these tables to the region which is used > > for grant table(or the region found by the same way) while it's not used > > when it boots with ACPI. These regions are not used by Xen and will not > > be used by Dom0 either currently. But as you say, it will be wrong if > > Dom0 memory is not 1:1 mapped. > > Will you remember in 6 months why you wrote the code like that? > > My point on the previous mail is you don't describe what you did, > neither in the code nor in the commit message. > > Most of the place in the code are trying to avoid the assumption that > DOM0 is using direct mapped. If not, we always have a comment/commit > message explaining why we are doing like that and the implication (see > the grant table example [1]). > > > So how about below idea: > > We still copy these tables to Dom0 RAM space but when we create > > EFI_MMAP_TABLE, we remove the space occupied by these tables from the > > EfiConventionalMemory descriptor. > > As you don't need the grant table region, why don't you re-use it fopr > your tables? It may also be possible that we have some space just after > for the EFI table. I think that the current approach is good, please just extend the in-code comment in patch #40.