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Thu, 16 May 2024 02:24:50 -0700 (PDT) Message-ID: Date: Thu, 16 May 2024 11:24:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3 (resend) 06/19] x86: Add a boot option to enable and disable the direct map Content-Language: en-US To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: Elias El Yandouzi , xen-devel@lists.xenproject.org, julien@xen.org, pdurrant@amazon.com, dwmw@amazon.com, Hongyan Xia , Andrew Cooper , George Dunlap , Stefano Stabellini , Julien Grall References: <20240513134046.82605-1-eliasely@amazon.com> <20240513134046.82605-7-eliasely@amazon.com> <086f1bbe-2b86-493e-8936-81f420500672@suse.com> From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 16.05.2024 11:19, Roger Pau Monné wrote: > On Wed, May 15, 2024 at 03:54:51PM +0200, Jan Beulich wrote: >> On 14.05.2024 11:20, Roger Pau Monné wrote: >>> On Mon, May 13, 2024 at 01:40:33PM +0000, Elias El Yandouzi wrote: >>>> --- a/docs/misc/xen-command-line.pandoc >>>> +++ b/docs/misc/xen-command-line.pandoc >>>> @@ -799,6 +799,18 @@ that enabling this option cannot guarantee anything beyond what underlying >>>> hardware guarantees (with, where available and known to Xen, respective >>>> tweaks applied). >>>> >>>> +### directmap (x86) >>>> +> `= ` >>>> + >>>> +> Default: `true` >>>> + >>>> +Enable or disable the directmap region in Xen. >>> >>> Enable or disable fully populating the directmap region in Xen. >> >> Elias, would you please take care to address earlier review comments >> before sending a new version? This and ... >> >>>> + >>>> +By default, Xen creates the directmap region which maps physical memory >>> ^ all? >>>> +in that region. Setting this to no will sparsely populate the directmap, >>> >>> "Setting this to no" => "Disabling this option will sparsely..." >> >> ... this is what I had already asked for in reply to v2, of course with >> different wording. >> >>>> --- a/xen/arch/x86/setup.c >>>> +++ b/xen/arch/x86/setup.c >>>> @@ -1517,6 +1517,8 @@ void asmlinkage __init noreturn __start_xen(unsigned long mbi_p) >>>> if ( highmem_start ) >>>> xenheap_max_mfn(PFN_DOWN(highmem_start - 1)); >>>> >>>> + printk("Booting with directmap %s\n", has_directmap() ? "on" : "off"); >>> >>> IMO this wants to be printed as part of the speculation mitigations, see >>> print_details() in spec_ctrl.c >> >> And not "on" / "off", but "full" / "sparse" (and word order changed accordingly) >> perhaps. > > I've been thinking about this, and I'm leaning towards calling this > new mode "ondemand" rather than "sparse". The fact that the direct > map ends up sparely populated is a consequence of populating it on > demand, and hence the later would be more descriptive IMO. > > (Same for the Kconfig option then ONDEMAND_DIRECTMAP, or some such) Fine with me, fwiw. Jan