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Smith" , Frediano Ziglio , Alejandro Vallejo , Xen-devel References: <20241113093058.1562447-1-andrew.cooper3@citrix.com> <20241113093058.1562447-2-andrew.cooper3@citrix.com> <5f58dda2-1619-4416-b711-c600367d6f47@suse.com> Content-Language: en-US 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 13.11.2024 12:19, Andrew Cooper wrote: > On 13/11/2024 10:20 am, Jan Beulich wrote: >> On 13.11.2024 10:30, Andrew Cooper wrote: >>> --- a/xen/arch/x86/include/asm/trampoline.h >>> +++ b/xen/arch/x86/include/asm/trampoline.h >>> @@ -37,12 +37,63 @@ >>> * manually as part of placement. >>> */ >>> >>> +/* >>> + * Layout of the trampoline. Logical areas, in ascending order: >>> + * >>> + * 1) AP boot: >>> + * >>> + * The INIT-SIPI-SIPI entrypoint. This logic is stack-less so the identity >>> + * mapping (which must be executable) can at least be Read Only. >>> + * >>> + * 2) S3 resume: >>> + * >>> + * The S3 wakeup logic may need to interact with the BIOS, so needs a >>> + * stack. The stack pointer is set to trampoline_phys + 4k and clobbers an >>> + * undefined part of the the boot trampoline. The stack is only used with >>> + * paging disabled. >>> + * >>> + * 3) Boot trampoline: >>> + * >>> + * This region houses various data used by the AP/S3 paths too. >> This is confusing to have here - isn't the boot part (that isn't in the >> same page as the tail of the AP/S3 region) being boot-time only, and hence >> unavailable for S3 and post-boot AP bringup? Both here and with the numbers >> in the description - what position did you use as separator between 2) and >> 3)? >> >> Then again it may be just me who is confused: Didn't we, at some point, limit >> the resident trampoline to just one page? Was that only a plan, or a patch >> that never was committed? > > The positioning of various things is rather complicated. > > Only a single 4k page is mapped into idle_pg_table[]. > > But, the AP/S3 path use: >   trampoline_cpu_started >   idt_48 >   gdt_48 >   trampoline_xen_phys_start >   trampoline_misc_enable_off >   trampoline_efer > > Which is beyond the content of wakeup.S.  The GDT in particular needs to > stay valid with paging enabled, to load __HYPERVISOR_CS. > > We have /* From here on early boot only. */ in trampoline.S but that > seems to be the extent of checking.  Everything needed for AP/S3 is in > the first 0x229. I was fearing it might be as weak. We probably want to gain a symbol there, for use in another linker script assertion. Jan