From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7E7B3388371 for ; Tue, 5 May 2026 11:38:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777981120; cv=none; b=jFh7IOBDu+cv3UbEITGHgsBrFI81pdj2K3W+DH4pZpIVOsFXIGhmc9U2Fql2qluFgWKbcmw7khg243uXXj6o8A0jjB6LQziU3JSwn2akdmIcN16ZINKvm31YRLibfrsnaxaNXut1MQwnd68uuivfGNCWiXRpQ41EQT8MQDGTp+E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777981120; c=relaxed/simple; bh=g1YQ8S4VPD7bLF9CRGQo7I4DxCi1ih33xBj9CSwW1Yk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=g8XvAk9p6F6OzC3qxN2nrqTUi83vT4LzTp/jJYRZ6rJsrtS7BR5he92KUsWa6VdYFAMq2EsHSOeCrWPg4Q4lf9YLIpdtoXOr0L9Ld6rLeNnAtwc0ac29uuehGMtyOLmYjTCb9uwme3TwW/VT/PWtzbN6llKpJCAE/tVm7znAfiU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=IhaS/OSk; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=GTpo7ZI3; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IhaS/OSk"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="GTpo7ZI3" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1777981117; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=UmcpW4CRfawEMyZUweO0e7YA2eoyQ5QeRsWWHrnqWI8=; b=IhaS/OSkg7C+Hl/Xs++9o5hTKyg1eB3eqDDj2j8RIjgsTu24l78mTxlxHk/xkmzu02wj9z yZ7ryC442QqpDaGS+V2TGhadS8+hvoyaLEL6QmOJbCEh1X3of0X0dzQMxixxkuKEiWsW6V U0O1CAnY8rgUgOr0FFjTBySz4yiE1nA= Received: from mail-yx1-f72.google.com (mail-yx1-f72.google.com [74.125.224.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-609-m_d-UQz6OfmHFjAacSiGqg-1; Tue, 05 May 2026 07:38:36 -0400 X-MC-Unique: m_d-UQz6OfmHFjAacSiGqg-1 X-Mimecast-MFC-AGG-ID: m_d-UQz6OfmHFjAacSiGqg_1777981116 Received: by mail-yx1-f72.google.com with SMTP id 956f58d0204a3-649df163c11so7125678d50.1 for ; Tue, 05 May 2026 04:38:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1777981116; x=1778585916; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to; bh=UmcpW4CRfawEMyZUweO0e7YA2eoyQ5QeRsWWHrnqWI8=; b=GTpo7ZI37vOgwO7EgTVAwEB4ouagrq7h9U/cA5B8xwr81mR4RCe95eR7lQYI8qE0wl xxCuk0LtI3grFeBf2yqRoNaiDzc+et5SodhyV1VoNmZjZSVVpGKYGpSJGtQFT6yYPI8C omoaghup9Ulqq36z+2bqRmb3SYYOGTBaQPfPfAjlfp/n8Vam6eBMySKu/lVTI9U634hv /bYn1WggUrmpL+lAyCrmSNLVPJUP5uT1ss4bpkW/d+UGz4Q98S+wmgw+leP/By5SI1i0 yGU5uolOPgos4vZtc2tI3GioiULurJP01MxCa4o/i7bhzpxXXyqN02emRU7Ees1ljtrP OyRw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777981116; x=1778585916; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=UmcpW4CRfawEMyZUweO0e7YA2eoyQ5QeRsWWHrnqWI8=; b=jViE+Q5iKxEeW3M3Cotypp7Tphbq5A83PIoHBIxLnClsR03AyJh9EkzCSj2olwkMkF qh6kngkVVvv6ae/939z+HOY1x/Tw47Z0AlnOtoVSauqrimffsSdFuE13wDNkK9FR+hAa jMwNu41jUth9qHH+b6eOm+5gf4bcLEqvbpictDG4xpr5gmwt6BCHYMnrnTsq/rT9/jzY hmocrI5yHqhG5xbvl+3jTW3NfuCM+9OOP8QNURfu1DCozsT/hwp+Jsg9mWey6RoahwvE YKUAlerM9dkdm1EXuug+pTuQ0yIGacVLCcpjnsXQBY17Lswq5kTK66C+RUUcsqG2rD+i gKgA== X-Forwarded-Encrypted: i=1; AFNElJ+rlv/y2i6lMxyUYI4oOr32aBos0r2dyVEzoWrVCU2UAuK+QY2Mo9z1ZItvsJ6sAU6SWwg=@vger.kernel.org X-Gm-Message-State: AOJu0YxEnhn/vtP2ouR4stiDWMbB9JifCzRBlgWlOrYMW4rLbK7UG/wc H6siY1Texps9WSimeNs3cGy4NbekGH2WFd3zGoQAVgpReCbVWzblN3B6c2oISdaa047gZlF3L+L uxUPhR2Ouy7XA09pY8GOKWhn/SVd7vX5SWTMuztUXnRFbK/dTNfyi2A== X-Gm-Gg: AeBDievpYrJpdCE0zBnOwCPKQj+t1DVYYLrBNXJWvAJlo6z6qN2ZlKkCzqsDRxJv4M4 MLRM33co5A3B9nL+W+rHdrDBHBnn0jPI5wc22eFZi6cmA2DXIDH2/G6xWLGysynPpFRUq4ilOtn TlOd+ZZEDwxE0TrbRCDvcYSeEyV9k3pqratpXktyKWGICwdSBrhdGVrF/wNrDnO1q3JsVJNNeum yCTUrP4Ah/l44lAf6fTqeLmsBEG4KOZkZNmLzTHcBt1DwJM0MKMI6qnPShlLYOhyYsE8MVrs8tn GEl1ElMxiycTBFJSk9dVOfNDRcgc7k4n03/WCaYEqwvQNO91CRSGiMSUfvs4PnsURF23rzXAQKb lOEmHmoZ30kURDR+sWPgZLdKKDYU1KQ== X-Received: by 2002:a05:690e:4349:b0:658:a18:cdf0 with SMTP id 956f58d0204a3-65c3da71355mr10839879d50.29.1777981115652; Tue, 05 May 2026 04:38:35 -0700 (PDT) X-Received: by 2002:a05:690e:4349:b0:658:a18:cdf0 with SMTP id 956f58d0204a3-65c3da71355mr10839664d50.29.1777981110414; Tue, 05 May 2026 04:38:30 -0700 (PDT) Received: from [192.168.0.9] ([47.64.115.164]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-65c2e1bb5adsm6870038d50.7.2026.05.05.04.38.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 May 2026 04:38:29 -0700 (PDT) Message-ID: <48384da2-7eb5-4044-bc3a-201b09d9cf81@redhat.com> Date: Tue, 5 May 2026 13:38:26 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: intel_iommu unit test is also failing To: "Michael S. Tsirkin" Cc: =?UTF-8?Q?Cl=C3=A9ment_MATHIEU--DRIF?= , Peter Xu , Paolo Bonzini , "kvm@vger.kernel.org" , Yi Liu References: <8aa24294-439f-4484-b6fc-9327b6fd0306@redhat.com> <600b025e-602e-4128-9679-f53f32b96e8e@redhat.com> <96f57df07e6d39e30557357142b2212e0ea26af4.camel@bull.com> <0abf41c113c9425ea4c73a108db22f28290fa395.camel@bull.com> <13002aef21dec62205c252f3d12bb42ea59cf287.camel@bull.com> <6b338140-873c-4303-bdd1-633d69f4a971@redhat.com> <20260505061927-mutt-send-email-mst@kernel.org> <20260505065122-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Thomas Huth Autocrypt: addr=thuth@redhat.com; keydata= xsFNBFH7eUwBEACzyOXKU+5Pcs6wNpKzrlJwzRl3VGZt95VCdb+FgoU9g11m7FWcOafrVRwU yYkTm9+7zBUc0sW5AuPGR/dp3pSLX/yFWsA/UB4nJsHqgDvDU7BImSeiTrnpMOTXb7Arw2a2 4CflIyFqjCpfDM4MuTmzTjXq4Uov1giGE9X6viNo1pxyEpd7PanlKNnf4PqEQp06X4IgUacW tSGj6Gcns1bCuHV8OPWLkf4hkRnu8hdL6i60Yxz4E6TqlrpxsfYwLXgEeswPHOA6Mn4Cso9O 0lewVYfFfsmokfAVMKWzOl1Sr0KGI5T9CpmRfAiSHpthhHWnECcJFwl72NTi6kUcUzG4se81 O6n9d/kTj7pzTmBdfwuOZ0YUSqcqs0W+l1NcASSYZQaDoD3/SLk+nqVeCBB4OnYOGhgmIHNW 0CwMRO/GK+20alxzk//V9GmIM2ACElbfF8+Uug3pqiHkVnKqM7W9/S1NH2qmxB6zMiJUHlTH gnVeZX0dgH27mzstcF786uPcdEqS0KJuxh2kk5IvUSL3Qn3ZgmgdxBMyCPciD/1cb7/Ahazr 3ThHQXSHXkH/aDXdfLsKVuwDzHLVSkdSnZdt5HHh75/NFHxwaTlydgfHmFFwodK8y/TjyiGZ zg2Kje38xnz8zKn9iesFBCcONXS7txENTzX0z80WKBhK+XSFJwARAQABzR5UaG9tYXMgSHV0 aCA8dGh1dGhAcmVkaGF0LmNvbT7CwXgEEwECACIFAlVgX6oCGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAAoJEC7Z13T+cC21EbIP/ii9cvT2HHGbFRl8HqGT6+7Wkb+XLMqJBMAIGiQK QIP3xk1HPTsLfVG0ao4hy/oYkGNOP8+ubLnZen6Yq3zAFiMhQ44lvgigDYJo3Ve59gfe99KX EbtB+X95ODARkq0McR6OAsPNJ7gpEUzfkQUUJTXRDQXfG/FX303Gvk+YU0spm2tsIKPl6AmV 1CegDljzjycyfJbk418MQmMu2T82kjrkEofUO2a24ed3VGC0/Uz//XCR2ZTo+vBoBUQl41BD eFFtoCSrzo3yPFS+w5fkH9NT8ChdpSlbNS32NhYQhJtr9zjWyFRf0Zk+T/1P7ECn6gTEkp5k ofFIA4MFBc/fXbaDRtBmPB0N9pqTFApIUI4vuFPPO0JDrII9dLwZ6lO9EKiwuVlvr1wwzsgq zJTPBU3qHaUO4d/8G+gD7AL/6T4zi8Jo/GmjBsnYaTzbm94lf0CjXjsOX3seMhaE6WAZOQQG tZHAO1kAPWpaxne+wtgMKthyPLNwelLf+xzGvrIKvLX6QuLoWMnWldu22z2ICVnLQChlR9d6 WW8QFEpo/FK7omuS8KvvopFcOOdlbFMM8Y/8vBgVMSsK6fsYUhruny/PahprPbYGiNIhKqz7 UvgyZVl4pBFjTaz/SbimTk210vIlkDyy1WuS8Zsn0htv4+jQPgo9rqFE4mipJjy/iboDzsFN BFH7eUwBEAC2nzfUeeI8dv0C4qrfCPze6NkryUflEut9WwHhfXCLjtvCjnoGqFelH/PE9NF4 4VPSCdvD1SSmFVzu6T9qWdcwMSaC+e7G/z0/AhBfqTeosAF5XvKQlAb9ZPkdDr7YN0a1XDfa +NgA+JZB4ROyBZFFAwNHT+HCnyzy0v9Sh3BgJJwfpXHH2l3LfncvV8rgFv0bvdr70U+On2XH 5bApOyW1WpIG5KPJlDdzcQTyptOJ1dnEHfwnABEfzI3dNf63rlxsGouX/NFRRRNqkdClQR3K gCwciaXfZ7ir7fF0u1N2UuLsWA8Ei1JrNypk+MRxhbvdQC4tyZCZ8mVDk+QOK6pyK2f4rMf/ WmqxNTtAVmNuZIwnJdjRMMSs4W4w6N/bRvpqtykSqx7VXcgqtv6eqoDZrNuhGbekQA0sAnCJ VPArerAZGArm63o39me/bRUQeQVSxEBmg66yshF9HkcUPGVeC4B0TPwz+HFcVhheo6hoJjLq knFOPLRj+0h+ZL+D0GenyqD3CyuyeTT5dGcNU9qT74bdSr20k/CklvI7S9yoQje8BeQAHtdV cvO8XCLrpGuw9SgOS7OP5oI26a0548M4KldAY+kqX6XVphEw3/6U1KTf7WxW5zYLTtadjISB X9xsRWSU+Yqs3C7oN5TIPSoj9tXMoxZkCIHWvnqGwZ7JhwARAQABwsFfBBgBAgAJBQJR+3lM AhsMAAoJEC7Z13T+cC21hPAQAIsBL9MdGpdEpvXs9CYrBkd6tS9mbaSWj6XBDfA1AEdQkBOn ZH1Qt7HJesk+qNSnLv6+jP4VwqK5AFMrKJ6IjE7jqgzGxtcZnvSjeDGPF1h2CKZQPpTw890k fy18AvgFHkVk2Oylyexw3aOBsXg6ukN44vIFqPoc+YSU0+0QIdYJp/XFsgWxnFIMYwDpxSHS 5fdDxUjsk3UBHZx+IhFjs2siVZi5wnHIqM7eK9abr2cK2weInTBwXwqVWjsXZ4tq5+jQrwDK cvxIcwXdUTLGxc4/Z/VRH1PZSvfQxdxMGmNTGaXVNfdFZjm4fz0mz+OUi6AHC4CZpwnsliGV ODqwX8Y1zic9viSTbKS01ZNp175POyWViUk9qisPZB7ypfSIVSEULrL347qY/hm9ahhqmn17 Ng255syASv3ehvX7iwWDfzXbA0/TVaqwa1YIkec+/8miicV0zMP9siRcYQkyTqSzaTFBBmqD oiT+z+/E59qj/EKfyce3sbC9XLjXv3mHMrq1tKX4G7IJGnS989E/fg6crv6NHae9Ckm7+lSs IQu4bBP2GxiRQ+NV3iV/KU3ebMRzqIC//DCOxzQNFNJAKldPe/bKZMCxEqtVoRkuJtNdp/5a yXFZ6TfE1hGKrDBYAm4vrnZ4CXFSBDllL59cFFOJCkn4Xboj/aVxxJxF30bn In-Reply-To: <20260505065122-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 05/05/2026 12.53, Michael S. Tsirkin wrote: > On Tue, May 05, 2026 at 12:34:41PM +0200, Thomas Huth wrote: >> On 05/05/2026 12.23, Michael S. Tsirkin wrote: >>> On Tue, May 05, 2026 at 11:45:17AM +0200, Thomas Huth wrote: >>>> On 05/05/2026 11.27, Clément MATHIEU--DRIF wrote: >>>>> I had a bit more time to hook into qemu to check the root cause. >>>>> >>>>> It seems that testb issues a single byte read (out of the valid size range), as we can see on the following breakpoint: >>>>> >>>>> ``` >>>>> Thread 6 "CPU 0/TCG" hit Breakpoint 2, memory_region_dispatch_read (mr=0x55d72883cb30, addr=152, pval=0x7f62d25f4590, op=MO_BSWAP, attrs=...) at ../system/memory.c:1473 >>>>> 1473 unsigned size = memop_size(op); >>>>> (gdb) n >>>>> 1474 MemTxResult r; >>>>> (gdb) p size >>>>> $1 = 1 >>>>> (gdb) >>>>> ``` >>>> >>>> Ouch! That's an excellent finding, Clément ... so GCC 16 is "smart" enough >>>> to see that we only want to test the lowest bit here, so it optimizes the >>>> code to access only one byte of memory instead of 4 bytes... which would be >>>> ok for normal memory, but not for an MMIO register :-/ >>>> >>>> Ugly work-around, to force GCC to read 32 bits: >>>> >>>> diff --git a/lib/asm-generic/io.h b/lib/asm-generic/io.h >>>> --- a/lib/asm-generic/io.h >>>> +++ b/lib/asm-generic/io.h >>>> @@ -38,7 +38,9 @@ static inline u16 __raw_readw(const volatile void *addr) >>>> #ifndef __raw_readl >>>> static inline u32 __raw_readl(const volatile void *addr) >>>> { >>>> - return *(const volatile u32 *)addr; >>>> + u32 val = *(const volatile u32 *)addr; >>>> + asm volatile ("\n" : : "r"(addr)); >>>> + return val; >>>> } >>>> #endif >>>> >>>> ... but I wonder whether this should rather be treated as a bug in GCC >>>> instead, since it should IMHO really not change the access size for a >>>> volatile memory access? >>>> >>>> Thomas >>> >>> Wouldn't this break linux generally? >>> >>> #ifndef __READ_ONCE >>> #define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x)) >>> #endif >> >> I asked myself the very same question, but after googling for "GCC 16 linux >> kernel" issues, I did not find anything related... there is likely something >> specific to kvm-unit-tests in here... >> >> Thomas > > > This seems to be pertinent: > https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html > > -ffuse-ops-with-volatile-access > Allow limited optimization of operations with volatile memory access when doing so does not change the semantics outlined in See When is a Volatile Object Accessed?. > > The default is -ffuse-ops-with-volatile-access > > implemented here: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122343 > > Try disabling? -fno-fuse-ops-with-volatile-access Thanks, this seems to fix the issue, indeed! Would you like to send a patch for it? Thomas