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AJvYcCXaTvsyZyoZPFtcOSpCIUCdY7KS7JFu9ZSIZb/GRlbAH1msECNwzKoaKxjeTNqA3q8KOjS8xc36m5uJzbcjw30kjDZJVSpbrnyNNt/ADiI= X-Gm-Message-State: AOJu0YwkQ15e2dhfmDZr8d2H7V15pXtzo3/ARc9s/91Id6qp53IOYigI Qo41i4n6eL2ylO4WJxPJmZoa98wDDiAaWgEpXTOQGmfCzWfUZRJ+F7pYZkbJ9B4= X-Google-Smtp-Source: AGHT+IH+I8Iq3Pr3UNAYqRuieBkDvhYHoUyY6bwV6Li/Jilx8Qb+Vt4k6+/STo6TNi35Q1e6PelghA== X-Received: by 2002:a2e:9619:0:b0:2ef:2e3f:35da with SMTP id 38308e7fff4ca-2f12ee634famr48998341fa.45.1722268344464; Mon, 29 Jul 2024 08:52:24 -0700 (PDT) Message-ID: <5aad5f48-e32e-4a59-bcef-05adec0ecbec@citrix.com> Date: Mon, 29 Jul 2024 16:52:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/22] x86/dom0: only disable SMAP for the PV dom0 build To: Jan Beulich , Roger Pau Monne Cc: alejandro.vallejo@cloud.com, xen-devel@lists.xenproject.org References: <20240726152206.28411-1-roger.pau@citrix.com> <20240726152206.28411-4-roger.pau@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 29/07/2024 12:53 pm, Jan Beulich wrote: > On 26.07.2024 17:21, Roger Pau Monne wrote: >> The PVH dom0 builder doesn't switch page tables and has no need to run with >> SMAP disabled. >> >> Put the SMAP disabling close to the code region where it's necessary, as it >> then becomes obvious why switch_cr3_cr4() is required instead of >> write_ptbase(). >> >> Note removing SMAP from cr4_pv32_mask is not required, as we never jump into >> guest context, and hence updating the value of cr4_pv32_mask is not relevant. > I'm okay-ish with that being dropped, but iirc the goal was to keep the > variable in sync with CPU state. Removing SMAP from cr4_pv32_mask is necessary. Otherwise IST vectors will reactive SMAP behind the back of the dombuilder. This will probably only manifest in practice in a CONFIG_PV32=y build, and with a poorly timed NMI. ~Andrew