From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59366) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dxQmg-0001Uo-Ag for qemu-devel@nongnu.org; Thu, 28 Sep 2017 00:50:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dxQmc-0003Fa-DZ for qemu-devel@nongnu.org; Thu, 28 Sep 2017 00:50:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49464) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dxQmc-0003FQ-7K for qemu-devel@nongnu.org; Thu, 28 Sep 2017 00:50:46 -0400 References: <20170927170027.8539-1-david@redhat.com> <20170927170027.8539-3-david@redhat.com> From: Thomas Huth Message-ID: <466fa6a0-ac91-66aa-aabb-a15a8ac62e0f@redhat.com> Date: Thu, 28 Sep 2017 06:50:39 +0200 MIME-Version: 1.0 In-Reply-To: <20170927170027.8539-3-david@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH RFC 2/3] s390x/tcg: low-address protection support List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Hildenbrand , qemu-devel@nongnu.org Cc: cohuck@redhat.com, Christian Borntraeger , Alexander Graf , Richard Henderson On 27.09.2017 19:00, David Hildenbrand wrote: > This is a neat way to implement low address protection, whereby > only the first 512 bytes of the first two pages (each 4096 bytes) of > every address space are protected. > > Store a tec of 0 for the access exception, this is what is defined by > Enhanced Suppression on Protection in case of a low address protection > (Bit 61 set to 0, rest undefined). > > We have to make sure to to pass the access address, not the masked page > address into mmu_translate*(). > > Drop the check from testblock. So we can properly test this via > kvm-unit-tests. > > This will check every access going through one of the MMUs. > > Signed-off-by: David Hildenbrand > --- > target/s390x/excp_helper.c | 3 +- > target/s390x/mem_helper.c | 8 ---- > target/s390x/mmu_helper.c | 96 +++++++++++++++++++++++++++++----------------- > 3 files changed, 62 insertions(+), 45 deletions(-) [...] > diff --git a/target/s390x/mmu_helper.c b/target/s390x/mmu_helper.c > index 9daa0fd8e2..44a15449d2 100644 > --- a/target/s390x/mmu_helper.c > +++ b/target/s390x/mmu_helper.c > @@ -106,6 +106,37 @@ static void trigger_page_fault(CPUS390XState *env, target_ulong vaddr, > trigger_access_exception(env, type, ilen, tec); > } > > +/* check whether the address would be proteted by Low-Address Protection */ > +static bool is_low_address(uint64_t addr) > +{ > + return addr < 512 || (addr >= 4096 && addr < 4607); > +} I like the check from the kernel sources better: static inline int is_low_address(unsigned long ga) { /* Check for address ranges 0..511 and 4096..4607 */ return (ga & ~0x11fful) == 0; } ... that might result in slightly faster code (depending on the compiler, of course). Thomas