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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id w15sm5543737pfc.220.2021.10.15.11.05.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Oct 2021 11:05:51 -0700 (PDT) Date: Fri, 15 Oct 2021 18:05:47 +0000 From: Sean Christopherson To: Brijesh Singh Cc: x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Joerg Roedel , Tom Lendacky , "H. Peter Anvin" , Ard Biesheuvel , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Andy Lutomirski , Dave Hansen , Sergio Lopez , Peter Gonda , Peter Zijlstra , Srinivas Pandruvada , David Rientjes , Dov Murik , Tobin Feldman-Fitzthum , Borislav Petkov , Michael Roth , Vlastimil Babka , "Kirill A . Shutemov" , Andi Kleen , tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com Subject: Re: [PATCH Part2 v5 05/45] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction Message-ID: References: <20210820155918.7518-1-brijesh.singh@amd.com> <20210820155918.7518-6-brijesh.singh@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210820155918.7518-6-brijesh.singh@amd.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 20, 2021, Brijesh Singh wrote: > diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c > index f383d2a89263..8627c49666c9 100644 > --- a/arch/x86/kernel/sev.c > +++ b/arch/x86/kernel/sev.c > @@ -2419,3 +2419,75 @@ int snp_lookup_rmpentry(u64 pfn, int *level) > return !!rmpentry_assigned(e); > } > EXPORT_SYMBOL_GPL(snp_lookup_rmpentry); > + > +int psmash(u64 pfn) > +{ > + unsigned long paddr = pfn << PAGE_SHIFT; Probably better to use __pfn_to_phys()? > + int ret; > + > + if (!pfn_valid(pfn)) > + return -EINVAL; > + > + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP)) Shouldn't this be a WARN_ON_ONCE()? > + return -ENXIO; > + > + /* Binutils version 2.36 supports the PSMASH mnemonic. */ > + asm volatile(".byte 0xF3, 0x0F, 0x01, 0xFF" > + : "=a"(ret) > + : "a"(paddr) > + : "memory", "cc"); > + > + return ret; I don't like returning the raw result from hardware; it's mostly works because hardware also uses '0' for success, but it will cause confusion should hardware ever set bit 31. There are also failures that likely should never happen unless there's a kernel bug, e.g. I suspect we can do: if (WARN_ON_ONCE(ret == FAIL_INPUT)) return -EINVAL; if (WARN_ON_ONCE(ret == FAIL_PERMISSION)) return -EPERM; .... or if all errors are "impossible" if (WARN_ON_ONCE(ret)) return snp_error_code_to_errno(ret); FAIL_INUSE and FAIL_OVERLAP also need further discussion. It's not clear to me that two well-behaved callers can't encounter collisions due to the 2mb <=> 4kb interactions. If collisions between well-behaved callers are possible, then this helper likely needs some form of serialization. Either, the concurrency rules for RMP access need explicit and lengthy documentation.