From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tom Lendacky Subject: Re: [RFC PATCH v2 08/32] x86: Use PAGE_KERNEL protection for ioremap of memory page Date: Thu, 16 Mar 2017 15:04:42 -0500 Message-ID: <413f12e9-818a-745d-374b-3dbc439e972c@amd.com> References: <148846752022.2349.13667498174822419498.stgit@brijesh-build-machine> <148846761276.2349.4899767672892365544.stgit@brijesh-build-machine> <20170307145954.l2fqy5s5h65wbtyz@pd.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Brijesh Singh Return-path: In-Reply-To: <20170307145954.l2fqy5s5h65wbtyz@pd.tnic> Sender: owner-linux-mm@kvack.org List-Id: linux-crypto.vger.kernel.org On 3/7/2017 8:59 AM, Borislav Petkov wrote: > On Thu, Mar 02, 2017 at 10:13:32AM -0500, Brijesh Singh wrote: >> From: Tom Lendacky >> >> In order for memory pages to be properly mapped when SEV is active, we >> need to use the PAGE_KERNEL protection attribute as the base protection. >> This will insure that memory mapping of, e.g. ACPI tables, receives the >> proper mapping attributes. >> >> Signed-off-by: Tom Lendacky >> --- > >> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c >> index c400ab5..481c999 100644 >> --- a/arch/x86/mm/ioremap.c >> +++ b/arch/x86/mm/ioremap.c >> @@ -151,7 +151,15 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr, >> pcm = new_pcm; >> } >> >> + /* >> + * If the page being mapped is in memory and SEV is active then >> + * make sure the memory encryption attribute is enabled in the >> + * resulting mapping. >> + */ >> prot = PAGE_KERNEL_IO; >> + if (sev_active() && page_is_mem(pfn)) > > Hmm, a resource tree walk per ioremap call. This could get expensive for > ioremap-heavy workloads. > > __ioremap_caller() gets called here during boot 55 times so not a whole > lot but I wouldn't be surprised if there were some nasty use cases which > ioremap a lot. > > ... > >> diff --git a/kernel/resource.c b/kernel/resource.c >> index 9b5f044..db56ba3 100644 >> --- a/kernel/resource.c >> +++ b/kernel/resource.c >> @@ -518,6 +518,46 @@ int __weak page_is_ram(unsigned long pfn) >> } >> EXPORT_SYMBOL_GPL(page_is_ram); >> >> +/* >> + * This function returns true if the target memory is marked as >> + * IORESOURCE_MEM and IORESOUCE_BUSY and described as other than >> + * IORES_DESC_NONE (e.g. IORES_DESC_ACPI_TABLES). >> + */ >> +static int walk_mem_range(unsigned long start_pfn, unsigned long nr_pages) >> +{ >> + struct resource res; >> + unsigned long pfn, end_pfn; >> + u64 orig_end; >> + int ret = -1; >> + >> + res.start = (u64) start_pfn << PAGE_SHIFT; >> + res.end = ((u64)(start_pfn + nr_pages) << PAGE_SHIFT) - 1; >> + res.flags = IORESOURCE_MEM | IORESOURCE_BUSY; >> + orig_end = res.end; >> + while ((res.start < res.end) && >> + (find_next_iomem_res(&res, IORES_DESC_NONE, true) >= 0)) { >> + pfn = (res.start + PAGE_SIZE - 1) >> PAGE_SHIFT; >> + end_pfn = (res.end + 1) >> PAGE_SHIFT; >> + if (end_pfn > pfn) >> + ret = (res.desc != IORES_DESC_NONE) ? 1 : 0; >> + if (ret) >> + break; >> + res.start = res.end + 1; >> + res.end = orig_end; >> + } >> + return ret; >> +} > > So the relevant difference between this one and walk_system_ram_range() > is this: > > - ret = (*func)(pfn, end_pfn - pfn, arg); > + ret = (res.desc != IORES_DESC_NONE) ? 1 : 0; > > so it seems to me you can have your own *func() pointer which does that > IORES_DESC_NONE comparison. And then you can define your own workhorse > __walk_memory_range() which gets called by both walk_mem_range() and > walk_system_ram_range() instead of almost duplicating them. > > And looking at walk_system_ram_res(), that one looks similar too except > the pfn computation. But AFAICT the pfn/end_pfn things are computed from > res.start and res.end so it looks to me like all those three functions > are crying for unification... I'll take a look at what it takes to consolidate these with a pre-patch. Then I'll add the new support. Thanks, Tom > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org