From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH v2] xen: arm: rework placement of fdt in initial dom0 memory map Date: Fri, 13 Sep 2013 16:18:18 +0100 Message-ID: <52332CBA.5090205@linaro.org> References: <1379082418-22871-1-git-send-email-ian.campbell@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1379082418-22871-1-git-send-email-ian.campbell@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: stefano.stabellini@eu.citrix.com, tim@xen.org, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 09/13/2013 03:26 PM, Ian Campbell wrote: > The 32-bit Linux kernel uses its lowmem direct mapping to access the FDT. The > lowmem mapping is around 0.75GiB but varies depending on the kernel's .config. > Our current scheme of loading the FDT as high as 4GB therefore fails with > larger amounts of dom0 RAM. > > The upstream documentation has recently been update to provide more guidance > . In > accordance with this load the kernel just below 128MiB (aligned to 2MB) and > the FDT just above, or if there is less RAM available then as high as > possible. > > Signed-off-by: Ian Campbell > --- > v2: Use the kernels own reported size rather than the size of the module. This > is consistent with the amount we will actually copy (zimage.len) > v1: This is technically v2 of "xen: arm: load FDT below 0.5G" > --- > xen/arch/arm/domain_build.c | 16 +++++++++++----- > xen/arch/arm/kernel.c | 27 ++++++++++++++++++++++++--- > 2 files changed, 35 insertions(+), 8 deletions(-) > > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c > index 77e2a61..172c985 100644 > --- a/xen/arch/arm/domain_build.c > +++ b/xen/arch/arm/domain_build.c > @@ -503,14 +503,20 @@ static int prepare_dtb(struct domain *d, struct kernel_info *kinfo) > if ( ret < 0 ) > goto err; > > + /* Actual new size */ > + new_size = fdt_totalsize(kinfo->fdt); > + > /* > - * DTB must be load below 4GiB and far enough from linux (Linux uses > - * the space after it to decompress) > - * Load the DTB at the end of the first bank, while ensuring it is > - * also below 4G > + * DTB must be loaded such that it does not conflict with the > + * kernel decompressor. For 32-bit Linux Documentation/arm/Booting > + * recommends just after the 128MB boundary while for 64-bit Linux > + * the recommendation in Documentation/arm64/booting.txt is below > + * 512MB. Place at 128MB, (or, if we have less RAM, as high as > + * possible) in order to satisfy both. > */ > end = kinfo->mem.bank[0].start + kinfo->mem.bank[0].size; > - end = MIN(1ull << 32, end); > + end = MIN(kinfo->mem.bank[0].start + (128<<20) + new_size, end); > + > kinfo->dtb_paddr = end - fdt_totalsize(kinfo->fdt); Can you use new_size here? > /* Align the address to 2Mb. Linux only requires 4 byte alignment */ > kinfo->dtb_paddr &= ~((2 << 20) - 1); I have noticed that the check below is wrong if ( fdt_totalsize(...) > end ) Can you fix the check in this patch? > diff --git a/xen/arch/arm/kernel.c b/xen/arch/arm/kernel.c > index f12f895..e4c0981 100644 > --- a/xen/arch/arm/kernel.c > +++ b/xen/arch/arm/kernel.c > @@ -211,11 +211,32 @@ static int kernel_try_zimage32_prepare(struct kernel_info *info, > info->zimage.kernel_addr = addr; > > /* > - * If start is zero, the zImage is position independent -- load it > - * at 32k from start of RAM. > + * If start is zero, the zImage is position independent, in this > + * case Documentation/arm/Booting recommends loading below 128MiB > + * and above 32MiB. Load it as high as possible within these > + * constraints, while also avoiding the DTB. > */ > if (start == 0) > - info->zimage.load_addr = info->mem.bank[0].start + 0x8000; > + { > + paddr_t load_end; > + > + load_end = info->mem.bank[0].start + info->mem.bank[0].size; > + load_end = MIN(info->mem.bank[0].start + (128<<20), load_end); > + > + /* > + * FDT is loaded above 128M or as high as possible, so the > + * only way we can clash is if we have <=128MB, in which case > + * FDT will be right at the end and so dtb_paddr will be below > + * the proposed kernel load address. Move the kernel down if > + * necessary. > + */ > + if ( load_end >= info->dtb_paddr ) > + load_end = info->dtb_paddr; > + > + info->zimage.load_addr = load_end - end + start; Actually start is always equals to 0, so you don't need to add it. In the future, we will need some check here to verify the kernel belongs to bank 0 and start won't. > + /* Align to 2MB */ > + info->zimage.load_addr &= ~((2 << 20) - 1); > + } > else > info->zimage.load_addr = start; > info->zimage.len = end - start; > -- Julien Grall