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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> 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: <20241113093058.1562447-2-andrew.cooper3@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 13.11.2024 10:30, Andrew Cooper wrote: > This is, to the best of my knowledge, accurate. I am providing no comment on > how sane I believe it to be. > > At the time of writing, the sizes of the regions are: > > offset size > AP: 0x0000 0x00b0 > S3: 0x00b0 0x0140 > Boot: 0x01f0 0x1780 > Heap: 0x1970 0xe690 > Stack: 0xf000 0x1000 > > and wakeup_stack overlays boot_edd_info. > > Signed-off-by: Andrew Cooper > --- > CC: Jan Beulich > CC: Roger Pau Monné > CC: Daniel P. Smith > CC: Frediano Ziglio > CC: Alejandro Vallejo > --- > xen/arch/x86/include/asm/trampoline.h | 55 ++++++++++++++++++++++++++- > 1 file changed, 53 insertions(+), 2 deletions(-) > > diff --git a/xen/arch/x86/include/asm/trampoline.h b/xen/arch/x86/include/asm/trampoline.h > index 8c1e0b48c2c9..d801bea400dc 100644 > --- 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 boot > + * trampoline collects data from the BIOS (E820/EDD/EDID/etc), so needs a > + * stack. The stack pointer is set to trampoline_phys + 64k and has 4k > + * space reserved. > + * > + * 4) Heap space: > + * > + * The first 1k of heap space is statically allocated for VESA information. > + * > + * The remainder of the heap is used by reloc(), logic which is otherwise > + * outside of the trampoline, to collect the bootloader metadata (cmdline, > + * module list, etc). It does so with a bump allocator starting from the > + * end of the heap and allocating backwards. > + * > + * 5) Boot stack: > + * > + * 4k of space is reserved for the boot stack, at trampoline_phys + 64k. Perhaps add "ending" to clarify it doesn't go beyond +64k? It's being expressed ... > + * Therefore, when placed, it looks somewhat like this: > + * > + * +--- trampoline_phys > + * v > + * |<-------------------------------64K------------------------------->| > + * |<-----4K----->| |<---4K--->| > + * +----+----+----+-+---------------------------------------+----------+ > + * | AP | S3 | Boot | Heap | Stack | > + * +----+----+------+---------------------------------------+----------+ > + * ^ <~~^ ^ <~~^ <~~^ > + * | | +- trampoline_end[] | | > + * | +--- S3 Stack reloc() allocator -+ | > + * +------------------ trampoline_start[] Boot Stack ------------+ > + */ ... by this scheme, but could still do with being made explicit, just to avoid ambiguity or suspicion of things have gone stale again. Jan